Thursday, March 31, 2011
Tuesday, March 29, 2011
Friday, March 11, 2011
Hibernate Stored Procedure call
Hibernate call store procedure
In Hibernate, there are three approaches to call a database store procedure.
1. Native SQL – createSQLQuery
You can use createSQLQuery() to call a store procedure directly.
Query query = session.createSQLQuery(
"CALL GetStocks(:stockCode)")
.addEntity(Stock.class)
.setParameter("stockCode", "7277");
List result = query.list();
for(int i=0; i
System.out.println(stock.getStockCode());
}
2. NamedNativeQuery in annotation
Declare your store procedure inside the @NamedNativeQueries annotation.
//Stock.java
...
@NamedNativeQueries({
@NamedNativeQuery(
name = "callStockStoreProcedure",
query = "CALL GetStocks(:stockCode)",
resultClass = Stock.class
)
})
@Entity
@Table(name = "stock")
public class Stock implements java.io.Serializable {
...
Call it with getNamedQuery().
Query query = session.getNamedQuery("callStockStoreProcedure")
.setParameter("stockCode", "7277");
List result = query.list();
for(int i=0; i
System.out.println(stock.getStockCode());
}
3. sql-query in XML mapping file
Declare your store procedure inside the “sql-query” tag.
...
...
Call it with getNamedQuery().
Query query = session.getNamedQuery("callStockStoreProcedure")
.setParameter("stockCode", "7277");
List result = query.list();
for(int i=0; i
System.out.println(stock.getStockCode());
}
Conclusion
The above three approaches are doing the same thing, call a store procedure in database. There are not much big different between the three approaches, which method you choose is depend on your personal prefer.
In Hibernate, there are three approaches to call a database store procedure.
1. Native SQL – createSQLQuery
You can use createSQLQuery() to call a store procedure directly.
Query query = session.createSQLQuery(
"CALL GetStocks(:stockCode)")
.addEntity(Stock.class)
.setParameter("stockCode", "7277");
List result = query.list();
for(int i=0; i
System.out.println(stock.getStockCode());
}
2. NamedNativeQuery in annotation
Declare your store procedure inside the @NamedNativeQueries annotation.
//Stock.java
...
@NamedNativeQueries({
@NamedNativeQuery(
name = "callStockStoreProcedure",
query = "CALL GetStocks(:stockCode)",
resultClass = Stock.class
)
})
@Entity
@Table(name = "stock")
public class Stock implements java.io.Serializable {
...
Call it with getNamedQuery().
Query query = session.getNamedQuery("callStockStoreProcedure")
.setParameter("stockCode", "7277");
List result = query.list();
for(int i=0; i
System.out.println(stock.getStockCode());
}
3. sql-query in XML mapping file
Declare your store procedure inside the “sql-query” tag.
...
...
Call it with getNamedQuery().
Query query = session.getNamedQuery("callStockStoreProcedure")
.setParameter("stockCode", "7277");
List result = query.list();
for(int i=0; i
System.out.println(stock.getStockCode());
}
Conclusion
The above three approaches are doing the same thing, call a store procedure in database. There are not much big different between the three approaches, which method you choose is depend on your personal prefer.
Thursday, March 10, 2011
WSDL Structure
http://msdn.microsoft.com/en-us/library/ms996486.aspx
----------------------
WSDL Document Structure
A WSDL document is an XML document that adheres to the WSDL XML schema. The WSDL schema is available at http://schemas.xmlsoap.org/wsdl/. Theoretically, WSDL can be used to describe any kind of Web service. In this document, only Web services that are SOAP based and compliant with the WS-I Basic Profile 1.0. are described.
The WSDL document is divided into six major elements which come from the “http://schemas.xmlsoap.org/wsdl/” namespace.
The definitions element MUST be the root element of all WSDL documents. It defines the name of the web service, declares multiple namespaces used throughout the remainder of the document, and contains all the service elements described here.
The types element describes all the data types used between the client and server. WSDL is not tied exclusively to a specific typing system, but it uses the W3C XML Schema specification as its default choice. If the service uses only XML Schema built-in simple types, such as strings and integers, the types element is not required.
The message element describes a one-way message, whether it is a single message request or a single message response. It defines the name of the message and contains zero or more message elements, which can refer to message parameters or message return values.
The portType element combines multiple message elements to form a complete one-way or round-trip operation. For example, a portType can combine one request and one response message into a single request/response operation, most commonly used in SOAP services. Note that a portType can (and frequently does) define multiple operations.
The binding element describes the concrete specifics of how the service will be implemented on the wire. WSDL includes built-in extensions for defining SOAP services, and SOAP-specific information therefore goes here.
The service element defines the address for invoking the specified service. Most commonly, this includes a URL for invoking the SOAP service.
In addition to the six major elements, the WSDL specification also defines the following utility elements:
The documentation element is used to provide human-readable documentation and can be included inside any other WSDL element.
The import element is used to import other WSDL documents or XML Schemas. This enables more modular WSDL documents. For example, two WSDL documents can import the same basic elements and yet include their own service elements to make the same service available at two physical addresses. Note, however, that not all WSDL tools support the import functionality as of yet.
NOTE: The WSDL schema requires that all sections appear in a specific order: import, types, message, portType, binding, and service. Each abstract section may be in a separate file by itself and imported into the main document.
----------------------
WSDL Document Structure
A WSDL document is an XML document that adheres to the WSDL XML schema. The WSDL schema is available at http://schemas.xmlsoap.org/wsdl/. Theoretically, WSDL can be used to describe any kind of Web service. In this document, only Web services that are SOAP based and compliant with the WS-I Basic Profile 1.0. are described.
The WSDL document is divided into six major elements which come from the “http://schemas.xmlsoap.org/wsdl/” namespace.
The definitions element MUST be the root element of all WSDL documents. It defines the name of the web service, declares multiple namespaces used throughout the remainder of the document, and contains all the service elements described here.
The types element describes all the data types used between the client and server. WSDL is not tied exclusively to a specific typing system, but it uses the W3C XML Schema specification as its default choice. If the service uses only XML Schema built-in simple types, such as strings and integers, the types element is not required.
The message element describes a one-way message, whether it is a single message request or a single message response. It defines the name of the message and contains zero or more message
The portType element combines multiple message elements to form a complete one-way or round-trip operation. For example, a portType can combine one request and one response message into a single request/response operation, most commonly used in SOAP services. Note that a portType can (and frequently does) define multiple operations.
The binding element describes the concrete specifics of how the service will be implemented on the wire. WSDL includes built-in extensions for defining SOAP services, and SOAP-specific information therefore goes here.
The service element defines the address for invoking the specified service. Most commonly, this includes a URL for invoking the SOAP service.
In addition to the six major elements, the WSDL specification also defines the following utility elements:
The documentation element is used to provide human-readable documentation and can be included inside any other WSDL element.
The import element is used to import other WSDL documents or XML Schemas. This enables more modular WSDL documents. For example, two WSDL documents can import the same basic elements and yet include their own service elements to make the same service available at two physical addresses. Note, however, that not all WSDL tools support the import functionality as of yet.
NOTE: The WSDL schema requires that all sections appear in a specific order: import, types, message, portType, binding, and service. Each abstract section may be in a separate file by itself and imported into the main document.
Wednesday, March 9, 2011
Webservices Qs
Q) Why are webservices needed?
Interoperatability
Q) Distinguish the type of Webservices?
SOAP Based and Restful.
a) SOAP Webservices:
Practically only two types of SOAP based webservices are used .. RPC Encoded and Document Literal.
RPC: Information is sent in the form of the method calls and the parameters
Document Literal: Information is sent in the form of an actual xml document which can be validated against
xml schema at the other end.
b) Representational state transfer (REST):
GET,POST,PUT,DELETE
Q) What are the two approaches to create a webservice?
Top Down: From WSDL one generates the Java Classes
Bottom Up: From Java classes one generates the WSDL
Q) Few tools used in your project if you used webservices.
SOAP UI: Test the web service
Some times some of the back end services might not available , so you can create a mock response and run the webservice service from the soap ui. Then your program should hit the mock response and you can check the functionality.
Stylus Studio: Create the XML Schema and generate the binding classes.
Axis2: Create the web service
Q) Explain the use of Castor?
Castor is used to create the binding classes from the schema
XML over HTTP
Q) What is the use of WS Policy?
Applied in the Web services model, policy is used to convey conditions on an interaction between two Web service endpoints.
condition like:
1) security token shud be atleast once or is required so on..
Q) What is JAX - RS?
JAX-RS: Java API for RESTful Web Services is a Java API that provides support in creating web services according to the Representational State Transfer (REST) architectural style. JAX-RS uses annotations.
Interoperatability
Q) Distinguish the type of Webservices?
SOAP Based and Restful.
a) SOAP Webservices:
Practically only two types of SOAP based webservices are used .. RPC Encoded and Document Literal.
RPC: Information is sent in the form of the method calls and the parameters
Document Literal: Information is sent in the form of an actual xml document which can be validated against
xml schema at the other end.
b) Representational state transfer (REST):
GET,POST,PUT,DELETE
Q) What are the two approaches to create a webservice?
Top Down: From WSDL one generates the Java Classes
Bottom Up: From Java classes one generates the WSDL
Q) Few tools used in your project if you used webservices.
SOAP UI: Test the web service
Some times some of the back end services might not available , so you can create a mock response and run the webservice service from the soap ui. Then your program should hit the mock response and you can check the functionality.
Stylus Studio: Create the XML Schema and generate the binding classes.
Axis2: Create the web service
Q) Explain the use of Castor?
Castor is used to create the binding classes from the schema
XML over HTTP
Q) What is the use of WS Policy?
Applied in the Web services model, policy is used to convey conditions on an interaction between two Web service endpoints.
condition like:
1) security token shud be atleast once or is required so on..
Q) What is JAX - RS?
JAX-RS: Java API for RESTful Web Services is a Java API that provides support in creating web services according to the Representational State Transfer (REST) architectural style. JAX-RS uses annotations.
Tuesday, March 8, 2011
Spring Interview Questions
1. What is IOC (or Dependency Injection)?
The basic concept of the Inversion of Control pattern (also known as dependency injection) is that you do not create your objects but describe how they should be created. You don't directly connect your components and services together in code but describe which services are needed by which components in a configuration file. A container (in the case of the Spring framework, the IOC container) is then responsible for hooking it all up.
i.e., Applying IoC, objects are given their dependencies at creation time by some external entity that coordinates each object in the system. That is, dependencies are injected into objects. So, IoC means an inversion of responsibility with regard to how an object obtains references to collaborating objects.
2. What are the different types of IOC (dependency injection) ?
There are three types of dependency injection:
• Constructor Injection (e.g. Pico container, Spring etc): Dependencies are provided as constructor parameters.
• Setter Injection (e.g. Spring): Dependencies are assigned through JavaBeans properties (ex: setter methods).
• Interface Injection (e.g. Avalon): Injection is done through an interface.
Note: Spring supports only Constructor and Setter Injection
3. What are the benefits of IOC (Dependency Injection)?
Benefits of IOC (Dependency Injection) are as follows:
• Minimizes the amount of code in your application. With IOC containers you do not care about how services are created and how you get references to the ones you need. You can also easily add additional services by adding a new constructor or a setter method with little or no extra configuration.
• Make your application more testable by not requiring any singletons or JNDI lookup mechanisms in your unit test cases. IOC containers make unit testing and switching implementations very easy by manually allowing you to inject your own objects into the object under test.
• Loose coupling is promoted with minimal effort and least intrusive mechanism. The factory design pattern is more intrusive because components or services need to be requested explicitly whereas in IOC the dependency is injected into requesting piece of code. Also some containers promote the design to interfaces not to implementations design concept by encouraging managed objects to implement a well-defined service interface of your own.
• IOC containers support eager instantiation and lazy loading of services. Containers also provide support for instantiation of managed objects, cyclical dependencies, life cycles management, and dependency resolution between managed objects etc.
4. What is Spring ?
Spring is an open source framework created to address the complexity of enterprise application development. One of the chief advantages of the Spring framework is its layered architecture, which allows you to be selective about which of its components you use while also providing a cohesive framework for J2EE application development.
5. What are the advantages of Spring framework?
The advantages of Spring are as follows:
• Spring has layered architecture. Use what you need and leave you don't need now.
• Spring Enables POJO Programming. There is no behind the scene magic here. POJO programming enables continuous integration and testability.
• Dependency Injection and Inversion of Control Simplifies JDBC
• Open source and no vendor lock-in.
6. What are features of Spring ?
• Lightweight:
spring is lightweight when it comes to size and transparency. The basic version of spring framework is around 1MB. And the processing overhead is also very negligible.
• Inversion of control (IOC):
Loose coupling is achieved in spring using the technique Inversion of Control. The objects give their dependencies instead of creating or looking for dependent objects.
• Aspect oriented (AOP):
Spring supports Aspect oriented programming and enables cohesive development by separating application business logic from system services.
• Container:
Spring contains and manages the life cycle and configuration of application objects.
• MVC Framework:
Spring comes with MVC web application framework, built on core Spring functionality. This framework is highly configurable via strategy interfaces, and accommodates multiple view technologies like JSP, Velocity, Tiles, iText, and POI. But other frameworks can be easily used instead of Spring MVC Framework.
• Transaction Management:
Spring framework provides a generic abstraction layer for transaction management. This allowing the developer to add the pluggable transaction managers, and making it easy to demarcate transactions without dealing with low-level issues. Spring's transaction support is not tied to J2EE environments and it can be also used in container less environments.
• JDBC Exception Handling:
The JDBC abstraction layer of the Spring offers a meaningful exception hierarchy, which simplifies the error handling strategy. Integration with Hibernate, JDO, and iBATIS: Spring provides best Integration services with Hibernate, JDO and iBATIS
7. How many modules are there in Spring? What are they?
(Roll over to view the Image )
Spring comprises of seven modules. They are..
• The core container:
The core container provides the essential functionality of the Spring framework. A primary component of the core container is the BeanFactory, an implementation of the Factory pattern. The BeanFactory applies the Inversion of Control (IOC) pattern to separate an application's configuration and dependency specification from the actual application code.
• Spring context:
The Spring context is a configuration file that provides context information to the Spring framework. The Spring context includes enterprise services such as JNDI, EJB, e-mail, internalization, validation, and scheduling functionality.
• Spring AOP:
The Spring AOP module integrates aspect-oriented programming functionality directly into the Spring framework, through its configuration management feature. As a result you can easily AOP-enable any object managed by the Spring framework. The Spring AOP module provides transaction management services for objects in any Spring-based application. With Spring AOP you can incorporate declarative transaction management into your applications without relying on EJB components.
• Spring DAO:
The Spring JDBC DAO abstraction layer offers a meaningful exception hierarchy for managing the exception handling and error messages thrown by different database vendors. The exception hierarchy simplifies error handling and greatly reduces the amount of exception code you need to write, such as opening and closing connections. Spring DAO's JDBC-oriented exceptions comply to its generic DAO exception hierarchy.
• Spring ORM:
The Spring framework plugs into several ORM frameworks to provide its Object Relational tool, including JDO, Hibernate, and iBatis SQL Maps. All of these comply to Spring's generic transaction and DAO exception hierarchies.
• Spring Web module:
The Web context module builds on top of the application context module, providing contexts for Web-based applications. As a result, the Spring framework supports integration with Jakarta Struts. The Web module also eases the tasks of handling multi-part requests and binding request parameters to domain objects.
• Spring MVC framework:
The Model-View-Controller (MVC) framework is a full-featured MVC implementation for building Web applications. The MVC framework is highly configurable via strategy interfaces and accommodates numerous view technologies including JSP, Velocity, Tiles, iText, and POI.
8. What are the types of Dependency Injection Spring supports?>
• Setter Injection:
Setter-based DI is realized by calling setter methods on your beans after invoking a no-argument constructor or no-argument static factory method to instantiate your bean.
• Constructor Injection:
Constructor-based DI is realized by invoking a constructor with a number of arguments, each representing a collaborator.
9. What is Bean Factory ?
A BeanFactory is like a factory class that contains a collection of beans. The BeanFactory holds Bean Definitions of multiple beans within itself and then instantiates the bean whenever asked for by clients.
• BeanFactory is able to create associations between collaborating objects as they are instantiated. This removes the burden of configuration from bean itself and the beans client.
• BeanFactory also takes part in the life cycle of a bean, making calls to custom initialization and destruction methods.
10. What is Application Context?
A bean factory is fine to simple applications, but to take advantage of the full power of the Spring framework, you may want to move up to Springs more advanced container, the application context. On the surface, an application context is same as a bean factory.Both load bean definitions, wire beans together, and dispense beans upon request. But it also provides:
• A means for resolving text messages, including support for internationalization.
• A generic way to load file resources.
• Events to beans that are registered as listeners.
11. What is the difference between Bean Factory and Application Context ?
On the surface, an application context is same as a bean factory. But application context offers much more..
• Application contexts provide a means for resolving text messages, including support for i18n of those messages.
• Application contexts provide a generic way to load file resources, such as images.
• Application contexts can publish events to beans that are registered as listeners.
• Certain operations on the container or beans in the container, which have to be handled in a programmatic fashion with a bean factory, can be handled declaratively in an application context.
• ResourceLoader support: Spring’s Resource interface us a flexible generic abstraction for handling low-level resources. An application context itself is a ResourceLoader, Hence provides an application with access to deployment-specific Resource instances.
• MessageSource support: The application context implements MessageSource, an interface used to obtain localized messages, with the actual implementation being pluggable
12. What are the common implementations of the Application Context ?
The three commonly used implementation of 'Application Context' are
• ClassPathXmlApplicationContext : It Loads context definition from an XML file located in the classpath, treating context definitions as classpath resources. The application context is loaded from the application's classpath by using the code .
ApplicationContext context = new ClassPathXmlApplicationContext("bean.xml");
• FileSystemXmlApplicationContext : It loads context definition from an XML file in the filesystem. The application context is loaded from the file system by using the code .
ApplicationContext context = new FileSystemXmlApplicationContext("bean.xml");
• XmlWebApplicationContext : It loads context definition from an XML file contained within a web application.
13. How is a typical spring implementation look like ?
For a typical Spring Application we need the following files:
• An interface that defines the functions.
• An Implementation that contains properties, its setter and getter methods, functions etc.,
• Spring AOP (Aspect Oriented Programming)
• A XML file called Spring configuration file.
• Client program that uses the function.
14. What is the typical Bean life cycle in Spring Bean Factory Container ?
Bean life cycle in Spring Bean Factory Container is as follows:
• The spring container finds the bean’s definition from the XML file and instantiates the bean.
• Using the dependency injection, spring populates all of the properties as specified in the bean definition
• If the bean implements the BeanNameAware interface, the factory calls setBeanName() passing the bean’s ID.
• If the bean implements the BeanFactoryAware interface, the factory calls setBeanFactory(), passing an instance of itself.
• If there are any BeanPostProcessors associated with the bean, their post- ProcessBeforeInitialization() methods will be called.
• If an init-method is specified for the bean, it will be called.
• Finally, if there are any BeanPostProcessors associated with the bean, their postProcessAfterInitialization() methods will be called.
15. What do you mean by Bean wiring ?
The act of creating associations between application components (beans) within the Spring container is reffered to as Bean wiring.
16. What do you mean by Auto Wiring?
The Spring container is able to autowire relationships between collaborating beans. This means that it is possible to automatically let Spring resolve collaborators (other beans) for your bean by inspecting the contents of the BeanFactory. The autowiring functionality has five modes.
• no
• byName
• byType
• constructor
• autodirect
17. What is DelegatingVariableResolver?
Spring provides a custom JavaServer Faces VariableResolver implementation that extends the standard Java Server Faces managed beans mechanism which lets you use JSF and Spring together. This variable resolver is called as DelegatingVariableResolver
18. How to integrate Java Server Faces (JSF) with Spring?
JSF and Spring do share some of the same features, most noticeably in the area of IOC services. By declaring JSF managed-beans in the faces-config.xml configuration file, you allow the FacesServlet to instantiate that bean at startup. Your JSF pages have access to these beans and all of their properties.We can integrate JSF and Spring in two ways:
• DelegatingVariableResolver: Spring comes with a JSF variable resolver that lets you use JSF and Spring together.
"http://www.springframework.org/dtd/spring-beans.dtd">
org.springframework.web.jsf.DelegatingVariableResolver
The DelegatingVariableResolver will first delegate value lookups to the default resolver of the underlying JSF implementation, and then to Spring's 'business context' WebApplicationContext. This allows one to easily inject dependencies into one's JSF-managed beans.
• FacesContextUtils:custom VariableResolver works well when mapping one's properties to beans in faces-config.xml, but at times one may need to grab a bean explicitly. The FacesContextUtils class makes this easy. It is similar to WebApplicationContextUtils, except that it takes a FacesContext parameter rather than a ServletContext parameter.
ApplicationContext ctx = FacesContextUtils.getWebApplicationContext(FacesContext.getCurrentInstance());
19. What is Java Server Faces (JSF) - Spring integration mechanism?
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Spring provides a custom JavaServer Faces VariableResolver implementation that extends the standard JavaServer Faces managed beans mechanism. When asked to resolve a variable name, the following algorithm is performed:
• Does a bean with the specified name already exist in some scope (request, session, application)? If so, return it
• Is there a standard JavaServer Faces managed bean definition for this variable name? If so, invoke it in the usual way, and return the bean that was created.
• Is there configuration information for this variable name in the Spring WebApplicationContext for this application? If so, use it to create and configure an instance, and return that instance to the caller.
• If there is no managed bean or Spring definition for this variable name, return null instead.
• BeanFactory also takes part in the life cycle of a bean, making calls to custom initialization and destruction methods.
As a result of this algorithm, you can transparently use either JavaServer Faces or Spring facilities to create beans on demand.
20. What is Significance of JSF- Spring integration ?
Spring - JSF integration is useful when an event handler wishes to explicitly invoke the bean factory to create beans on demand, such as a bean that encapsulates the business logic to be performed when a submit button is pressed.
21. How to integrate your Struts application with Spring?
To integrate your Struts application with Spring, we have two options:
• Configure Spring to manage your Actions as beans, using the ContextLoaderPlugin, and set their dependencies in a Spring context file.
• Subclass Spring's ActionSupport classes and grab your Spring-managed beans explicitly using a getWebApplicationContext() method.
22. What are ORM’s Spring supports ?
Spring supports the following ORM’s :
• Hibernate
• iBatis
• JPA (Java Persistence API)
• TopLink
• JDO (Java Data Objects)
• OJB
23. What are the ways to access Hibernate using Spring ?
There are two approaches to Spring’s Hibernate integration:
• Inversion of Control with a HibernateTemplate and Callback
• Extending HibernateDaoSupport and Applying an AOP Interceptor
24. How to integrate Spring and Hibernate using HibernateDaoSupport?
Spring and Hibernate can integrate using Spring’s SessionFactory called LocalSessionFactory. The integration process is of 3 steps.
• Configure the Hibernate SessionFactory
• Extend your DAO Implementation from HibernateDaoSupport
• Wire in Transaction Support with AOP
25. What are Bean scopes in Spring Framework ?
The Spring Framework supports exactly five scopes (of which three are available only if you are using a web-aware ApplicationContext). The scopes supported are listed below:
Scope Description
singleton Scopes a single bean definition to a single object instance per Spring IoC container.
prototype Scopes a single bean definition to any number of object instances.
request Scopes a single bean definition to the lifecycle of a single HTTP request; that is each and every HTTP request will have its own instance of a bean created off the back of a single bean definition. Only valid in the context of a web-aware Spring ApplicationContext.
session Scopes a single bean definition to the lifecycle of a HTTP Session. Only valid in the context of a web-aware Spring ApplicationContext.
global session Scopes a single bean definition to the lifecycle of a global HTTP Session. Typically only valid when used in a portlet context. Only valid in the context of a web-aware Spring ApplicationContext.
26. What is AOP?
Aspect-oriented programming, or AOP, is a programming technique that allows programmers to modularize crosscutting concerns, or behavior that cuts across the typical divisions of responsibility, such as logging and transaction management. The core construct of AOP is the aspect, which encapsulates behaviors affecting multiple classes into reusable modules.
27. How the AOP used in Spring?
AOP is used in the Spring Framework: To provide declarative enterprise services, especially as a replacement for EJB declarative services. The most important such service is declarative transaction management, which builds on the Spring Framework's transaction abstraction.To allow users to implement custom aspects, complementing their use of OOP with AOP.
28. What do you mean by Aspect ?
A modularization of a concern that cuts across multiple objects. Transaction management is a good example of a crosscutting concern in J2EE applications. In Spring AOP, aspects are implemented using regular classes (the schema-based approach) or regular classes annotated with the @Aspect annotation (@AspectJ style).
29. What do you mean by JointPoint?
A point during the execution of a program, such as the execution of a method or the handling of an exception. In Spring AOP, a join point always represents a method execution.
30. What do you mean by Advice?
Action taken by an aspect at a particular join point. Different types of advice include "around," "before" and "after" advice. Many AOP frameworks, including Spring, model an advice as an interceptor, maintaining a chain of interceptors "around" the join point.
31. What are the types of Advice?
Types of advice:
• Before advice: Advice that executes before a join point, but which does not have the ability to prevent execution flow proceeding to the join point (unless it throws an exception).
• After returning advice: Advice to be executed after a join point completes normally: for example, if a method returns without throwing an exception.
• After throwing advice: Advice to be executed if a method exits by throwing an exception.
• After (finally) advice: Advice to be executed regardless of the means by which a join point exits (normal or exceptional return).
• Around advice: Advice that surrounds a join point such as a method invocation. This is the most powerful kind of advice. Around advice can perform custom behavior before and after the method invocation. It is also responsible for choosing whether to proceed to the join point or to shortcut the advised method execution by returning its own return value or throwing an exception
32. What are the types of the transaction management Spring supports ?
Spring Framework supports:
• Programmatic transaction management.
• Declarative transaction management.
33. What are the benefits of the Spring Framework transaction management ?
The Spring Framework provides a consistent abstraction for transaction management that delivers the following benefits:
• Provides a consistent programming model across different transaction APIs such as JTA, JDBC, Hibernate, JPA, and JDO.
• Supports declarative transaction management.
• Provides a simpler API for programmatic transaction management than a number of complex transaction APIs such as JTA.
• Integrates very well with Spring's various data access abstractions.
34. Why most users of the Spring Framework choose declarative transaction management ?
Most users of the Spring Framework choose declarative transaction management because it is the option with the least impact on application code, and hence is most consistent with the ideals of a non-invasive lightweight container.
35. Explain the similarities and differences between EJB CMT and the Spring Framework's declarative transaction
management ?
The basic approach is similar: it is possible to specify transaction behavior (or lack of it) down to individual method level. It is
possible to make a setRollbackOnly() call within a transaction context if necessary. The differences are:
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• Unlike EJB CMT, which is tied to JTA, the Spring Framework's declarative transaction management works in any environment. It can work with JDBC, JDO, Hibernate or other transactions under the covers, with configuration changes only.
• The Spring Framework enables declarative transaction management to be applied to any class, not merely special classes such as EJBs.
• The Spring Framework offers declarative rollback rules: this is a feature with no EJB equivalent. Both programmatic and declarative support for rollback rules is provided.
• The Spring Framework gives you an opportunity to customize transactional behavior, using AOP. With EJB CMT, you have no way to influence the container's transaction management other than setRollbackOnly().
• The Spring Framework does not support propagation of transaction contexts across remote calls, as do high-end application servers.
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37. When to use programmatic and declarative transaction management ?
Programmatic transaction management is usually a good idea only if you have a small number of transactional operations.
On the other hand, if your application has numerous transactional operations, declarative transaction management is usually worthwhile. It keeps transaction management out of business logic, and is not difficult to configure.
38. Explain about the Spring DAO support ?
The Data Access Object (DAO) support in Spring is aimed at making it easy to work with data access technologies like JDBC, Hibernate or JDO in a consistent way. This allows one to switch between the persistence technologies fairly easily and it also allows one to code without worrying about catching exceptions that are specific to each technology.
39. What are the exceptions thrown by the Spring DAO classes ?
Spring DAO classes throw exceptions which are subclasses ofDataAccessException(org.springframework.dao.DataAccessException).Spring provides a convenient translation from technology-specific exceptions like SQLExceptionto its own exception class hierarchy with the DataAccessException as the root exception. These exceptions wrap the original exception.
40. What is SQLExceptionTranslator ?
SQLExceptionTranslator, is an interface to be implemented by classes that can translate between SQLExceptions and Spring's own data-access-strategy-agnosticorg.springframework.dao.DataAccessException.
41. What is Spring's JdbcTemplate ?
Spring's JdbcTemplate is central class to interact with a database through JDBC. JdbcTemplate provides many convenience methods for doing things such as converting database data into primitives or objects, executing prepared and callable statements, and providing custom database error handling.
JdbcTemplate template = new JdbcTemplate(myDataSource);
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42. What is PreparedStatementCreator ?
PreparedStatementCreator:
• Is one of the most common used interfaces for writing data to database.
• Has one method – createPreparedStatement(Connection)
• Responsible for creating a PreparedStatement.
• Does not need to handle SQLExceptions.
43. What is SQLProvider ?
SQLProvider:
• Has one method – getSql()
• Typically implemented by PreparedStatementCreator implementers.
• Useful for debugging.
44. What is RowCallbackHandler ?
The RowCallbackHandler interface extracts values from each row of a ResultSet.
• Has one method – processRow(ResultSet)
• Called for each row in ResultSet.
• Typically stateful.
45. What are the differences between EJB and Spring ?
Spring and EJB feature comparison.
Feature EJB Spring
Transaction management • Must use a JTA transaction manager.
• Supports transactions that span remote method calls. • Supports multiple transaction environments through itsPlatformTransactionManager interface, including JTA, Hibernate, JDO, and JDBC.
• Does not natively support distributed transactions—it must be used with a JTA transaction manager.
Declarative transaction support • Can define transactions declaratively through the deployment descriptor.
• Can define transaction behavior per method or per class by using the wildcard character *.
• Cannot declaratively define rollback behavior—this must be done programmatically. • Can define transactions declaratively through the Spring configuration file or through class metadata.
• Can define which methods to apply transaction behavior explicitly or by using regular expressions.
• Can declaratively define rollback behavior per method and per exception type.
Persistence Supports programmatic bean-managed persistence and declarative container managed persistence. Provides a framework for integrating with several persistence technologies, including JDBC, Hibernate, JDO, and iBATIS.
Declarative security • Supports declarative security through users and roles. The management and implementation of users and roles is container specific.
• Declarative security is configured in the deployment descriptor. • No security implementation out-of-the box.
• Acegi, an open source security framework built on top of Spring, provides declarative security through the Spring configuration file or class metadata.
Distributed computing Provides container-managed remote method calls. Provides proxying for remote calls via RMI, JAX-RPC, and web services.
The basic concept of the Inversion of Control pattern (also known as dependency injection) is that you do not create your objects but describe how they should be created. You don't directly connect your components and services together in code but describe which services are needed by which components in a configuration file. A container (in the case of the Spring framework, the IOC container) is then responsible for hooking it all up.
i.e., Applying IoC, objects are given their dependencies at creation time by some external entity that coordinates each object in the system. That is, dependencies are injected into objects. So, IoC means an inversion of responsibility with regard to how an object obtains references to collaborating objects.
2. What are the different types of IOC (dependency injection) ?
There are three types of dependency injection:
• Constructor Injection (e.g. Pico container, Spring etc): Dependencies are provided as constructor parameters.
• Setter Injection (e.g. Spring): Dependencies are assigned through JavaBeans properties (ex: setter methods).
• Interface Injection (e.g. Avalon): Injection is done through an interface.
Note: Spring supports only Constructor and Setter Injection
3. What are the benefits of IOC (Dependency Injection)?
Benefits of IOC (Dependency Injection) are as follows:
• Minimizes the amount of code in your application. With IOC containers you do not care about how services are created and how you get references to the ones you need. You can also easily add additional services by adding a new constructor or a setter method with little or no extra configuration.
• Make your application more testable by not requiring any singletons or JNDI lookup mechanisms in your unit test cases. IOC containers make unit testing and switching implementations very easy by manually allowing you to inject your own objects into the object under test.
• Loose coupling is promoted with minimal effort and least intrusive mechanism. The factory design pattern is more intrusive because components or services need to be requested explicitly whereas in IOC the dependency is injected into requesting piece of code. Also some containers promote the design to interfaces not to implementations design concept by encouraging managed objects to implement a well-defined service interface of your own.
• IOC containers support eager instantiation and lazy loading of services. Containers also provide support for instantiation of managed objects, cyclical dependencies, life cycles management, and dependency resolution between managed objects etc.
4. What is Spring ?
Spring is an open source framework created to address the complexity of enterprise application development. One of the chief advantages of the Spring framework is its layered architecture, which allows you to be selective about which of its components you use while also providing a cohesive framework for J2EE application development.
5. What are the advantages of Spring framework?
The advantages of Spring are as follows:
• Spring has layered architecture. Use what you need and leave you don't need now.
• Spring Enables POJO Programming. There is no behind the scene magic here. POJO programming enables continuous integration and testability.
• Dependency Injection and Inversion of Control Simplifies JDBC
• Open source and no vendor lock-in.
6. What are features of Spring ?
• Lightweight:
spring is lightweight when it comes to size and transparency. The basic version of spring framework is around 1MB. And the processing overhead is also very negligible.
• Inversion of control (IOC):
Loose coupling is achieved in spring using the technique Inversion of Control. The objects give their dependencies instead of creating or looking for dependent objects.
• Aspect oriented (AOP):
Spring supports Aspect oriented programming and enables cohesive development by separating application business logic from system services.
• Container:
Spring contains and manages the life cycle and configuration of application objects.
• MVC Framework:
Spring comes with MVC web application framework, built on core Spring functionality. This framework is highly configurable via strategy interfaces, and accommodates multiple view technologies like JSP, Velocity, Tiles, iText, and POI. But other frameworks can be easily used instead of Spring MVC Framework.
• Transaction Management:
Spring framework provides a generic abstraction layer for transaction management. This allowing the developer to add the pluggable transaction managers, and making it easy to demarcate transactions without dealing with low-level issues. Spring's transaction support is not tied to J2EE environments and it can be also used in container less environments.
• JDBC Exception Handling:
The JDBC abstraction layer of the Spring offers a meaningful exception hierarchy, which simplifies the error handling strategy. Integration with Hibernate, JDO, and iBATIS: Spring provides best Integration services with Hibernate, JDO and iBATIS
7. How many modules are there in Spring? What are they?
(Roll over to view the Image )
Spring comprises of seven modules. They are..
• The core container:
The core container provides the essential functionality of the Spring framework. A primary component of the core container is the BeanFactory, an implementation of the Factory pattern. The BeanFactory applies the Inversion of Control (IOC) pattern to separate an application's configuration and dependency specification from the actual application code.
• Spring context:
The Spring context is a configuration file that provides context information to the Spring framework. The Spring context includes enterprise services such as JNDI, EJB, e-mail, internalization, validation, and scheduling functionality.
• Spring AOP:
The Spring AOP module integrates aspect-oriented programming functionality directly into the Spring framework, through its configuration management feature. As a result you can easily AOP-enable any object managed by the Spring framework. The Spring AOP module provides transaction management services for objects in any Spring-based application. With Spring AOP you can incorporate declarative transaction management into your applications without relying on EJB components.
• Spring DAO:
The Spring JDBC DAO abstraction layer offers a meaningful exception hierarchy for managing the exception handling and error messages thrown by different database vendors. The exception hierarchy simplifies error handling and greatly reduces the amount of exception code you need to write, such as opening and closing connections. Spring DAO's JDBC-oriented exceptions comply to its generic DAO exception hierarchy.
• Spring ORM:
The Spring framework plugs into several ORM frameworks to provide its Object Relational tool, including JDO, Hibernate, and iBatis SQL Maps. All of these comply to Spring's generic transaction and DAO exception hierarchies.
• Spring Web module:
The Web context module builds on top of the application context module, providing contexts for Web-based applications. As a result, the Spring framework supports integration with Jakarta Struts. The Web module also eases the tasks of handling multi-part requests and binding request parameters to domain objects.
• Spring MVC framework:
The Model-View-Controller (MVC) framework is a full-featured MVC implementation for building Web applications. The MVC framework is highly configurable via strategy interfaces and accommodates numerous view technologies including JSP, Velocity, Tiles, iText, and POI.
8. What are the types of Dependency Injection Spring supports?>
• Setter Injection:
Setter-based DI is realized by calling setter methods on your beans after invoking a no-argument constructor or no-argument static factory method to instantiate your bean.
• Constructor Injection:
Constructor-based DI is realized by invoking a constructor with a number of arguments, each representing a collaborator.
9. What is Bean Factory ?
A BeanFactory is like a factory class that contains a collection of beans. The BeanFactory holds Bean Definitions of multiple beans within itself and then instantiates the bean whenever asked for by clients.
• BeanFactory is able to create associations between collaborating objects as they are instantiated. This removes the burden of configuration from bean itself and the beans client.
• BeanFactory also takes part in the life cycle of a bean, making calls to custom initialization and destruction methods.
10. What is Application Context?
A bean factory is fine to simple applications, but to take advantage of the full power of the Spring framework, you may want to move up to Springs more advanced container, the application context. On the surface, an application context is same as a bean factory.Both load bean definitions, wire beans together, and dispense beans upon request. But it also provides:
• A means for resolving text messages, including support for internationalization.
• A generic way to load file resources.
• Events to beans that are registered as listeners.
11. What is the difference between Bean Factory and Application Context ?
On the surface, an application context is same as a bean factory. But application context offers much more..
• Application contexts provide a means for resolving text messages, including support for i18n of those messages.
• Application contexts provide a generic way to load file resources, such as images.
• Application contexts can publish events to beans that are registered as listeners.
• Certain operations on the container or beans in the container, which have to be handled in a programmatic fashion with a bean factory, can be handled declaratively in an application context.
• ResourceLoader support: Spring’s Resource interface us a flexible generic abstraction for handling low-level resources. An application context itself is a ResourceLoader, Hence provides an application with access to deployment-specific Resource instances.
• MessageSource support: The application context implements MessageSource, an interface used to obtain localized messages, with the actual implementation being pluggable
12. What are the common implementations of the Application Context ?
The three commonly used implementation of 'Application Context' are
• ClassPathXmlApplicationContext : It Loads context definition from an XML file located in the classpath, treating context definitions as classpath resources. The application context is loaded from the application's classpath by using the code .
ApplicationContext context = new ClassPathXmlApplicationContext("bean.xml");
• FileSystemXmlApplicationContext : It loads context definition from an XML file in the filesystem. The application context is loaded from the file system by using the code .
ApplicationContext context = new FileSystemXmlApplicationContext("bean.xml");
• XmlWebApplicationContext : It loads context definition from an XML file contained within a web application.
13. How is a typical spring implementation look like ?
For a typical Spring Application we need the following files:
• An interface that defines the functions.
• An Implementation that contains properties, its setter and getter methods, functions etc.,
• Spring AOP (Aspect Oriented Programming)
• A XML file called Spring configuration file.
• Client program that uses the function.
14. What is the typical Bean life cycle in Spring Bean Factory Container ?
Bean life cycle in Spring Bean Factory Container is as follows:
• The spring container finds the bean’s definition from the XML file and instantiates the bean.
• Using the dependency injection, spring populates all of the properties as specified in the bean definition
• If the bean implements the BeanNameAware interface, the factory calls setBeanName() passing the bean’s ID.
• If the bean implements the BeanFactoryAware interface, the factory calls setBeanFactory(), passing an instance of itself.
• If there are any BeanPostProcessors associated with the bean, their post- ProcessBeforeInitialization() methods will be called.
• If an init-method is specified for the bean, it will be called.
• Finally, if there are any BeanPostProcessors associated with the bean, their postProcessAfterInitialization() methods will be called.
15. What do you mean by Bean wiring ?
The act of creating associations between application components (beans) within the Spring container is reffered to as Bean wiring.
16. What do you mean by Auto Wiring?
The Spring container is able to autowire relationships between collaborating beans. This means that it is possible to automatically let Spring resolve collaborators (other beans) for your bean by inspecting the contents of the BeanFactory. The autowiring functionality has five modes.
• no
• byName
• byType
• constructor
• autodirect
17. What is DelegatingVariableResolver?
Spring provides a custom JavaServer Faces VariableResolver implementation that extends the standard Java Server Faces managed beans mechanism which lets you use JSF and Spring together. This variable resolver is called as DelegatingVariableResolver
18. How to integrate Java Server Faces (JSF) with Spring?
JSF and Spring do share some of the same features, most noticeably in the area of IOC services. By declaring JSF managed-beans in the faces-config.xml configuration file, you allow the FacesServlet to instantiate that bean at startup. Your JSF pages have access to these beans and all of their properties.We can integrate JSF and Spring in two ways:
• DelegatingVariableResolver: Spring comes with a JSF variable resolver that lets you use JSF and Spring together.
"http://www.springframework.org/dtd/spring-beans.dtd">
org.springframework.web.jsf.DelegatingVariableResolver
The DelegatingVariableResolver will first delegate value lookups to the default resolver of the underlying JSF implementation, and then to Spring's 'business context' WebApplicationContext. This allows one to easily inject dependencies into one's JSF-managed beans.
• FacesContextUtils:custom VariableResolver works well when mapping one's properties to beans in faces-config.xml, but at times one may need to grab a bean explicitly. The FacesContextUtils class makes this easy. It is similar to WebApplicationContextUtils, except that it takes a FacesContext parameter rather than a ServletContext parameter.
ApplicationContext ctx = FacesContextUtils.getWebApplicationContext(FacesContext.getCurrentInstance());
19. What is Java Server Faces (JSF) - Spring integration mechanism?
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Spring provides a custom JavaServer Faces VariableResolver implementation that extends the standard JavaServer Faces managed beans mechanism. When asked to resolve a variable name, the following algorithm is performed:
• Does a bean with the specified name already exist in some scope (request, session, application)? If so, return it
• Is there a standard JavaServer Faces managed bean definition for this variable name? If so, invoke it in the usual way, and return the bean that was created.
• Is there configuration information for this variable name in the Spring WebApplicationContext for this application? If so, use it to create and configure an instance, and return that instance to the caller.
• If there is no managed bean or Spring definition for this variable name, return null instead.
• BeanFactory also takes part in the life cycle of a bean, making calls to custom initialization and destruction methods.
As a result of this algorithm, you can transparently use either JavaServer Faces or Spring facilities to create beans on demand.
20. What is Significance of JSF- Spring integration ?
Spring - JSF integration is useful when an event handler wishes to explicitly invoke the bean factory to create beans on demand, such as a bean that encapsulates the business logic to be performed when a submit button is pressed.
21. How to integrate your Struts application with Spring?
To integrate your Struts application with Spring, we have two options:
• Configure Spring to manage your Actions as beans, using the ContextLoaderPlugin, and set their dependencies in a Spring context file.
• Subclass Spring's ActionSupport classes and grab your Spring-managed beans explicitly using a getWebApplicationContext() method.
22. What are ORM’s Spring supports ?
Spring supports the following ORM’s :
• Hibernate
• iBatis
• JPA (Java Persistence API)
• TopLink
• JDO (Java Data Objects)
• OJB
23. What are the ways to access Hibernate using Spring ?
There are two approaches to Spring’s Hibernate integration:
• Inversion of Control with a HibernateTemplate and Callback
• Extending HibernateDaoSupport and Applying an AOP Interceptor
24. How to integrate Spring and Hibernate using HibernateDaoSupport?
Spring and Hibernate can integrate using Spring’s SessionFactory called LocalSessionFactory. The integration process is of 3 steps.
• Configure the Hibernate SessionFactory
• Extend your DAO Implementation from HibernateDaoSupport
• Wire in Transaction Support with AOP
25. What are Bean scopes in Spring Framework ?
The Spring Framework supports exactly five scopes (of which three are available only if you are using a web-aware ApplicationContext). The scopes supported are listed below:
Scope Description
singleton Scopes a single bean definition to a single object instance per Spring IoC container.
prototype Scopes a single bean definition to any number of object instances.
request Scopes a single bean definition to the lifecycle of a single HTTP request; that is each and every HTTP request will have its own instance of a bean created off the back of a single bean definition. Only valid in the context of a web-aware Spring ApplicationContext.
session Scopes a single bean definition to the lifecycle of a HTTP Session. Only valid in the context of a web-aware Spring ApplicationContext.
global session Scopes a single bean definition to the lifecycle of a global HTTP Session. Typically only valid when used in a portlet context. Only valid in the context of a web-aware Spring ApplicationContext.
26. What is AOP?
Aspect-oriented programming, or AOP, is a programming technique that allows programmers to modularize crosscutting concerns, or behavior that cuts across the typical divisions of responsibility, such as logging and transaction management. The core construct of AOP is the aspect, which encapsulates behaviors affecting multiple classes into reusable modules.
27. How the AOP used in Spring?
AOP is used in the Spring Framework: To provide declarative enterprise services, especially as a replacement for EJB declarative services. The most important such service is declarative transaction management, which builds on the Spring Framework's transaction abstraction.To allow users to implement custom aspects, complementing their use of OOP with AOP.
28. What do you mean by Aspect ?
A modularization of a concern that cuts across multiple objects. Transaction management is a good example of a crosscutting concern in J2EE applications. In Spring AOP, aspects are implemented using regular classes (the schema-based approach) or regular classes annotated with the @Aspect annotation (@AspectJ style).
29. What do you mean by JointPoint?
A point during the execution of a program, such as the execution of a method or the handling of an exception. In Spring AOP, a join point always represents a method execution.
30. What do you mean by Advice?
Action taken by an aspect at a particular join point. Different types of advice include "around," "before" and "after" advice. Many AOP frameworks, including Spring, model an advice as an interceptor, maintaining a chain of interceptors "around" the join point.
31. What are the types of Advice?
Types of advice:
• Before advice: Advice that executes before a join point, but which does not have the ability to prevent execution flow proceeding to the join point (unless it throws an exception).
• After returning advice: Advice to be executed after a join point completes normally: for example, if a method returns without throwing an exception.
• After throwing advice: Advice to be executed if a method exits by throwing an exception.
• After (finally) advice: Advice to be executed regardless of the means by which a join point exits (normal or exceptional return).
• Around advice: Advice that surrounds a join point such as a method invocation. This is the most powerful kind of advice. Around advice can perform custom behavior before and after the method invocation. It is also responsible for choosing whether to proceed to the join point or to shortcut the advised method execution by returning its own return value or throwing an exception
32. What are the types of the transaction management Spring supports ?
Spring Framework supports:
• Programmatic transaction management.
• Declarative transaction management.
33. What are the benefits of the Spring Framework transaction management ?
The Spring Framework provides a consistent abstraction for transaction management that delivers the following benefits:
• Provides a consistent programming model across different transaction APIs such as JTA, JDBC, Hibernate, JPA, and JDO.
• Supports declarative transaction management.
• Provides a simpler API for programmatic transaction management than a number of complex transaction APIs such as JTA.
• Integrates very well with Spring's various data access abstractions.
34. Why most users of the Spring Framework choose declarative transaction management ?
Most users of the Spring Framework choose declarative transaction management because it is the option with the least impact on application code, and hence is most consistent with the ideals of a non-invasive lightweight container.
35. Explain the similarities and differences between EJB CMT and the Spring Framework's declarative transaction
management ?
The basic approach is similar: it is possible to specify transaction behavior (or lack of it) down to individual method level. It is
possible to make a setRollbackOnly() call within a transaction context if necessary. The differences are:
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• Unlike EJB CMT, which is tied to JTA, the Spring Framework's declarative transaction management works in any environment. It can work with JDBC, JDO, Hibernate or other transactions under the covers, with configuration changes only.
• The Spring Framework enables declarative transaction management to be applied to any class, not merely special classes such as EJBs.
• The Spring Framework offers declarative rollback rules: this is a feature with no EJB equivalent. Both programmatic and declarative support for rollback rules is provided.
• The Spring Framework gives you an opportunity to customize transactional behavior, using AOP. With EJB CMT, you have no way to influence the container's transaction management other than setRollbackOnly().
• The Spring Framework does not support propagation of transaction contexts across remote calls, as do high-end application servers.
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37. When to use programmatic and declarative transaction management ?
Programmatic transaction management is usually a good idea only if you have a small number of transactional operations.
On the other hand, if your application has numerous transactional operations, declarative transaction management is usually worthwhile. It keeps transaction management out of business logic, and is not difficult to configure.
38. Explain about the Spring DAO support ?
The Data Access Object (DAO) support in Spring is aimed at making it easy to work with data access technologies like JDBC, Hibernate or JDO in a consistent way. This allows one to switch between the persistence technologies fairly easily and it also allows one to code without worrying about catching exceptions that are specific to each technology.
39. What are the exceptions thrown by the Spring DAO classes ?
Spring DAO classes throw exceptions which are subclasses ofDataAccessException(org.springframework.dao.DataAccessException).Spring provides a convenient translation from technology-specific exceptions like SQLExceptionto its own exception class hierarchy with the DataAccessException as the root exception. These exceptions wrap the original exception.
40. What is SQLExceptionTranslator ?
SQLExceptionTranslator, is an interface to be implemented by classes that can translate between SQLExceptions and Spring's own data-access-strategy-agnosticorg.springframework.dao.DataAccessException.
41. What is Spring's JdbcTemplate ?
Spring's JdbcTemplate is central class to interact with a database through JDBC. JdbcTemplate provides many convenience methods for doing things such as converting database data into primitives or objects, executing prepared and callable statements, and providing custom database error handling.
JdbcTemplate template = new JdbcTemplate(myDataSource);
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42. What is PreparedStatementCreator ?
PreparedStatementCreator:
• Is one of the most common used interfaces for writing data to database.
• Has one method – createPreparedStatement(Connection)
• Responsible for creating a PreparedStatement.
• Does not need to handle SQLExceptions.
43. What is SQLProvider ?
SQLProvider:
• Has one method – getSql()
• Typically implemented by PreparedStatementCreator implementers.
• Useful for debugging.
44. What is RowCallbackHandler ?
The RowCallbackHandler interface extracts values from each row of a ResultSet.
• Has one method – processRow(ResultSet)
• Called for each row in ResultSet.
• Typically stateful.
45. What are the differences between EJB and Spring ?
Spring and EJB feature comparison.
Feature EJB Spring
Transaction management • Must use a JTA transaction manager.
• Supports transactions that span remote method calls. • Supports multiple transaction environments through itsPlatformTransactionManager interface, including JTA, Hibernate, JDO, and JDBC.
• Does not natively support distributed transactions—it must be used with a JTA transaction manager.
Declarative transaction support • Can define transactions declaratively through the deployment descriptor.
• Can define transaction behavior per method or per class by using the wildcard character *.
• Cannot declaratively define rollback behavior—this must be done programmatically. • Can define transactions declaratively through the Spring configuration file or through class metadata.
• Can define which methods to apply transaction behavior explicitly or by using regular expressions.
• Can declaratively define rollback behavior per method and per exception type.
Persistence Supports programmatic bean-managed persistence and declarative container managed persistence. Provides a framework for integrating with several persistence technologies, including JDBC, Hibernate, JDO, and iBATIS.
Declarative security • Supports declarative security through users and roles. The management and implementation of users and roles is container specific.
• Declarative security is configured in the deployment descriptor. • No security implementation out-of-the box.
• Acegi, an open source security framework built on top of Spring, provides declarative security through the Spring configuration file or class metadata.
Distributed computing Provides container-managed remote method calls. Provides proxying for remote calls via RMI, JAX-RPC, and web services.
Sunday, September 12, 2010
Good Java Questions
What is a platform?
A platform is the hardware or software environment in which a program runs. Most platforms can be described as a combination of the operating system and hardware, like Windows 2000/XP, Linux, Solaris, and MacOS.
What is the main difference between Java platform and other platforms?
The Java platform differs from most other platforms in that it's a software-only platform that runs on top of other hardware-based platforms.
The Java platform has two components:
The Java Virtual Machine (Java VM)
The Java Application Programming Interface (Java API)
What is the Java Virtual Machine?
The Java Virtual Machine is a software that can be ported onto various hardware-based platforms.
What is the Java API?
The Java API is a large collection of ready-made software components that provide many useful capabilities, such as graphical user interface (GUI) widgets.
What is the package?
The package is a Java namespace or part of Java libraries. The Java API is grouped into libraries of related classes and interfaces; these libraries are known as packages.
What is native code?
The native code is code that after you compile it, the compiled code runs on a specific hardware platform.
Is Java code slower than native code?
Not really. As a platform-independent environment, the Java platform can be a bit slower than native code. However, smart compilers, well-tuned interpreters, and just-in-time bytecode compilers can bring performance close to that of native code without threatening portability.
What is the serialization?
The serialization is a kind of mechanism that makes a class or a bean persistence by having its properties or fields and state information saved and restored to and from storage.
How to make a class or a bean serializable?
By implementing either the java.io.Serializable interface, or the java.io.Externalizable interface. As long as one class in a class's inheritance hierarchy implements Serializable or Externalizable, that class is serializable.
How many methods in the Serializable interface?
There is no method in the Serializable interface. The Serializable interface acts as a marker, telling the object serialization tools that your class is serializable.
How many methods in the Externalizable interface?
There are two methods in the Externalizable interface. You have to implement these two methods in order to make your class externalizable. These two methods are readExternal() and writeExternal().
What is the difference between Serializalble and Externalizable interface?
When you use Serializable interface, your class is serialized automatically by default. But you can override writeObject() and readObject() two methods to control more complex object serailization process. When you use Externalizable interface, you have a complete control over your class's serialization process.
What is a transient variable?
A transient variable is a variable that may not be serialized. If you don't want some field not to be serialized, you can mark that field transient or static.
Which containers use a border layout as their default layout?
The window, Frame and Dialog classes use a border layout as their default layout.
How are Observer and Observable used?
Objects that subclass the Observable class maintain a list of observers. When an Observable object is updated it invokes the update() method of each of its observers to notify the observers that it has changed state. The Observer interface is implemented by objects that observe Observable objects.
What are synchronized methods and synchronized statements?
Synchronized methods are methods that are used to control access to an object. A thread only executes a synchronized method after it has acquired the lock for the method's object or class. Synchronized statements are similar to synchronized methods. A synchronized statement can only be executed after a thread has acquired the lock for the object or class referenced in the synchronized statement.
What are three ways in which a thread can enter the waiting state?
A thread can enter the waiting state by invoking its sleep() method, by blocking on I/O, by unsuccessfully attempting to acquire an object's lock, or by invoking an object's wait() method. It can also enter the waiting state by invoking its (deprecated) suspend() method.
Can a lock be acquired on a class?
Yes, a lock can be acquired on a class. This lock is acquired on the class's Class object.
What's new with the stop(), suspend() and resume() methods in JDK 1.2?
The stop(), suspend() and resume() methods have been deprecated in JDK 1.2.
What is the preferred size of a component?
The preferred size of a component is the minimum component size that will allow the component to display normally.
What method is used to specify a container's layout?
The setLayout() method is used to specify a container's layout.
Which containers use a FlowLayout as their default layout?
The Panel and Applet classes use the FlowLayout as their default layout.
What state does a thread enter when it terminates its processing?
When a thread terminates its processing, it enters the dead state.
What is the Collections API?
The Collections API is a set of classes and interfaces that support operations on collections of objects.
What is the List interface?
The List interface provides support for ordered collections of objects.
How does Java handle integer overflows and underflows?
It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.
What is the Vector class?
The Vector class provides the capability to implement a growable array of objects
What modifiers may be used with an inner class that is a member of an outer class?
A (non-local) inner class may be declared as public, protected, private, static, final, or abstract.
If a method is declared as protected, where may the method be accessed?
A protected method may only be accessed by classes or interfaces of the same package or by subclasses of the class in which it is declared.
What is an Iterator interface?
The Iterator interface is used to step through the elements of a Collection.
How many bits are used to represent Unicode, ASCII, UTF-16, and UTF-8 characters?
Unicode requires 16 bits and ASCII require 7 bits. Although the ASCII character set uses only 7 bits, it is usually represented as 8 bits. UTF-8 represents characters using 8, 16, and 18 bit patterns. UTF-16 uses 16-bit and larger bit patterns.
What is the difference between yielding and sleeping?
When a task invokes its yield() method, it returns to the ready state. When a task invokes its sleep() method, it returns to the waiting state.
Is sizeof a keyword?
The sizeof operator is not a keyword.
What are wrapped classes?
Wrapped classes are classes that allow primitive types to be accessed as objects.
Does garbage collection guarantee that a program will not run out of memory?
No, it doesn't. It is possible for programs to use up memory resources faster than they are garbage collected. It is also possible for programs to create objects that are not subject to garbage collection
What is the difference between preemptive scheduling and time slicing?
Under preemptive scheduling, the highest priority task executes until it enters the waiting or dead states or a higher priority task comes into existence. Under time slicing, a task executes for a predefined slice of time and then reenters the pool of ready tasks. The scheduler then determines which task should execute next, based on priority and other factors.
Name Component subclasses that support painting.
The Canvas, Frame, Panel, and Applet classes support painting.
What is a native method?
A native method is a method that is implemented in a language other than Java.
How can you write a loop indefinitely?
for(;;)--for loop; while(true)--always true, etc.
Can an anonymous class be declared as implementing an interface and extending a class?
An anonymous class may implement an interface or extend a superclass, but may not be declared to do both.
What is the purpose of finalization?
The purpose of finalization is to give an unreachable object the opportunity to perform any cleanup processing before the object is garbage collected.
Which class is the superclass for every class.
Object
What invokes a thread's run() method?
After a thread is started, via its start() method or that of the Thread class, the JVM invokes the thread's run() method when the thread is initially executed.
What is the difference between the Boolean & operator and the && operator?
If an expression involving the Boolean & operator is evaluated, both operands are evaluated. Then the & operator is applied to the operand. When an expression involving the && operator is evaluated, the first operand is evaluated. If the first operand returns a value of true then the second operand is evaluated. The && operator is then applied to the first and second operands. If the first operand evaluates to false, the evaluation of the second operand is skipped.
Operator & has no chance to skip both sides evaluation and && operator does. If asked why, give details as above.
What is the GregorianCalendar class?
The GregorianCalendar provides support for traditional Western calendars.
What is the SimpleTimeZone class?
The SimpleTimeZone class provides support for a Gregorian calendar.
Which Container method is used to cause a container to be laid out and redisplayed?
validate()
What is the Properties class?
The properties class is a subclass of Hashtable that can be read from or written to a stream. It also provides the capability to specify a set of default values to be used.
What is the purpose of the Runtime class?
The purpose of the Runtime class is to provide access to the Java runtime system.
What is the purpose of the System class?
The purpose of the System class is to provide access to system resources.
What is the purpose of the finally clause of a try-catch-finally statement?
The finally clause is used to provide the capability to execute code no matter whether or not an exception is thrown or caught.
What is the Locale class?
The Locale class is used to tailor program output to the conventions of a particular geographic, political, or cultural region.
What must a class do to implement an interface?
It must provide all of the methods in the interface and identify the interface in its implements clause.
What is the purpose of the wait(), notify(), and notifyAll() methods?
The wait(),notify(), and notifyAll() methods are used to provide an efficient way for threads to communicate each other.
What is an abstract method?
An abstract method is a method whose implementation is deferred to a subclass. Or, a method that has no implementation (an interface of a method).
What is a static method?
A static method is a method that belongs to the class rather than any object of the class and doesn't apply to an object or even require that any objects of the class have been instantiated
What is a protected method?
A protected method is a method that can be accessed by any method in its package and inherited by any subclass of its class.
What are the high-level thread states?
The high-level thread states are ready, running, waiting, and dead.
What is the difference between a static and a non-static inner class?
A non-static inner class may have object instances that are associated with instances of the class's outer class. A static inner class does not have any object instances.
What is an object's lock and which object's have locks?
An object's lock is a mechanism that is used by multiple threads to obtain synchronized access to the object. A thread may execute a synchronized method of an object only after it has acquired the object's lock. All objects and classes have locks. A class's lock is acquired on the class's Class object.
When can an object reference be cast to an interface reference?
An object reference be cast to an interface reference when the object implements the referenced interface.
What is the difference between a Window and a Frame?
The Frame class extends Window to define a main application window that can have a menu bar.
What do heavy weight components mean?
Heavy weight components like Abstract Window Toolkit (AWT), depend on the local windowing toolkit. For example, java.awt.Button is a heavy weight component, when it is running on the Java platform for Unix platform, it maps to a real Motif button. In this relationship, the Motif button is called the peer to the java.awt.Button. If you create two Buttons, two peers and hence two Motif Buttons are also created. The Java platform communicates with the Motif Buttons using the Java Native Interface. For each and every component added to the application, there is an additional overhead tied to the local windowing system, which is why these components are called heavy weight.
Which package has light weight components?
javax.Swing package. All components in Swing, except JApplet, JDialog, JFrame and JWindow are lightweight components.
What are peerless components?
The peerless components are called light weight components.
What is the difference between the Font and FontMetrics classes?
The FontMetrics class is used to define implementation-specific properties, such as ascent and descent, of a Font object.
What happens when a thread cannot acquire a lock on an object?
If a thread attempts to execute a synchronized method or synchronized statement and is unable to acquire an object's lock, it enters the waiting state until the lock becomes available.
What is the difference between the Reader/Writer class hierarchy and the InputStream/OutputStream class hierarchy?
The Reader/Writer class hierarchy is character-oriented, and the InputStream/OutputStream class hierarchy is byte-oriented.
What classes of exceptions may be caught by a catch clause?
A catch clause can catch any exception that may be assigned to the Throwable type. This includes the Error and Exception types.
What is the difference between throw and throws keywords?
The throw keyword denotes a statement that causes an exception to be initiated. It takes the Exception object to be thrown as argument. The exception will be caught by an immediately encompassing try-catch construction or propagated further up the calling hierarchy.
The throws keyword is a modifier of a method that designates that exceptions may come out of the method, either by virtue of the method throwing the exception itself or because it fails to catch such exceptions that a method it calls may throw.
If a class is declared without any access modifiers, where may the class be accessed?
A class that is declared without any access modifiers is said to have package or friendly access. This means that the class can only be accessed by other classes and interfaces that are defined within the same package.
What is the Map interface?
The Map interface replaces the JDK 1.1 Dictionary class and is used associate keys with values.
Does a class inherit the constructors of its superclass?
A class does not inherit constructors from any of its superclasses.
Name primitive Java types.
The primitive types are byte, char, short, int, long, float, double, and boolean.
Which class should you use to obtain design information about an object?
The Class class is used to obtain information about an object's design.
How can a GUI component handle its own events?
A component can handle its own events by implementing the required event-listener interface and adding itself as its own event listener.
How are the elements of a GridBagLayout organized?
The elements of a GridBagLayout are organized according to a grid. However, the elements are of different sizes and may occupy more than one row or column of the grid. In addition, the rows and columns may have different sizes.
What advantage do Java's layout managers provide over traditional windowing systems?
Java uses layout managers to lay out components in a consistent manner across all windowing platforms. Since Java's layout managers aren't tied to absolute sizing and positioning, they are able to accommodate platform-specific differences among windowing systems.
What are the problems faced by Java programmers who don't use layout managers?
Without layout managers, Java programmers are faced with determining how their GUI will be displayed across multiple windowing systems and finding a common sizing and positioning that will work within the constraints imposed by each windowing system.
What is the difference between static and non-static variables?
A static variable is associated with the class as a whole rather than with specific instances of a class. Non-static variables take on unique values with each object instance.
What is the difference between the paint() and repaint() methods?
The paint() method supports painting via a Graphics object. The repaint() method is used to cause paint() to be invoked by the AWT painting thread.
What is the purpose of the File class?
The File class is used to create objects that provide access to the files and directories of a local file system.
How does multithreading take place on a computer with a single CPU?
The operating system's task scheduler allocates execution time to multiple tasks. By quickly switching between executing tasks, it creates the impression that tasks execute sequentially.
What restrictions are placed on method overloading?
Two methods may not have the same name and argument list but different return types.
What restrictions are placed on method overriding?
Overridden methods must have the same name, argument list, and return type. The overriding method may not limit the access of the method it overrides. The overriding method may not throw any exceptions that may not be thrown by the overridden method.
What is casting?
There are two types of casting, casting between primitive numeric types and casting between object references. Casting between numeric types is used to convert larger values, such as double values, to smaller values, such as byte values. Casting between object references is used to refer to an object by a compatible class, interface, or array type reference
Name Container classes. ?
Window, Frame, Dialog, FileDialog, Panel, Applet, or ScrollPane
What class allows you to read objects directly from a stream?
The ObjectInputStream class supports the reading of objects from input streams.
How are this() and super() used with constructors?
this() is used to invoke a constructor of the same class. super() is used to invoke a superclass constructor.
How is it possible for two String objects with identical values not to be equal under the == operator?
The == operator compares two objects to determine if they are the same object in memory. It is possible for two String objects to have the same value, but located indifferent areas of memory.
What an I/O filter?
An I/O filter is an object that reads from one stream and writes to another, usually altering the data in some way as it is passed from one stream to another.
What is the Set interface?
The Set interface provides methods for accessing the elements of a finite mathematical set. Sets do not allow duplicate elements.
What is the List interface?
The List interface provides support for ordered collections of objects.
What is the purpose of the enableEvents() method?
The enableEvents() method is used to enable an event for a particular object. Normally, an event is enabled when a listener is added to an object for a particular event. The enableEvents() method is used by objects that handle events by overriding their event-dispatch methods.
What is the difference between the File and RandomAccessFile classes?
The File class encapsulates the files and directories of the local file system. The RandomAccessFile class provides the methods needed to directly access data contained in any part of a file.
What interface must an object implement before it can be written to a stream as an object?
An object must implement the Serializable or Externalizable interface before it can be written to a stream as an object.
What is the ResourceBundle class?
The ResourceBundle class is used to store locale-specific resources that can be loaded by a program to tailor the program's appearance to the particular locale in which it is being run.
What is the difference between a Scrollbar and a ScrollPane?
A Scrollbar is a Component, but not a Container. A ScrollPane is a Container. A ScrollPane handles its own events and performs its own scrolling.
What is a Java package and how is it used?
A Java package is a naming context for classes and interfaces. A package is used to create a separate name space for groups of classes and interfaces. Packages are also used to organize related classes and interfaces into a single API unit and to control accessibility to these classes and interfaces.
What are the Object and Class classes used for?
The Object class is the highest-level class in the Java class hierarchy. The Class class is used to represent the classes and interfaces that are loaded by a Java program.
What is Serialization and deserialization?
Serialization is the process of writing the state of an object to a byte stream.
Deserialization is the process of restoring these objects.
What is tunnelling?
Tunnelling is a route to somewhere. For example, RMI tunnelling is a way to make RMI application get through firewall. In CS world, tunnelling means a way to transfer data.
Does the code in finally block get executed if there is an exception and a return statement in a catch block?
If an exception occurs and there is a return statement in catch block, the finally block is still executed. The finally block will not be executed when the System.exit(1) statement is executed earlier or the system shut down earlier or the memory is used up earlier before the thread goes to finally block.
How you restrict a user to cut and paste from the html page?
Using javaScript to lock keyboard keys. It is one of solutions.
Is Java a super set of JavaScript?
No. They are completely different. Some syntax may be similar.
What is a Container in a GUI?
A Container contains and arranges other components (including other containers) through the use of layout managers, which use specific layout policies to determine where components should go as a function of the size of the container.
How the object oriented approach helps us keep complexity of software development under control?
We can discuss such issue from the following aspects:
Objects allow procedures to be encapsulated with their data to reduce potential interference.
Inheritance allows well-tested procedures to be reused and enables changes to make once and have effect in all relevant places.
The well-defined separations of interface and implementation allows constraints to be imposed on inheriting classes while still allowing the flexibility of overriding and overloading.
What is polymorphism?
Polymorphism allows methods to be written that needn't be concerned about the specifics of the objects they will be applied to. That is, the method can be specified at a higher level of abstraction and can be counted on to work even on objects of yet unconceived classes.
What is design by contract?
The design by contract specifies the obligations of a method to any other methods that may use its services and also theirs to it. For example, the preconditions specify what the method required to be true when the method is called. Hence making sure that preconditions are. Similarly, post conditions specify what must be true when the method is finished, thus the called method has the responsibility of satisfying the post conditions.
In Java, the exception handling facilities support the use of design by contract, especially in the case of checked exceptions. The assert keyword can be used to make such contracts.
What are use cases?
A use case describes a situation that a program might encounter and what behavior the program should exhibit in that circumstance. It is part of the analysis of a program. The collection of use cases should, ideally, anticipate all the standard circumstances and many of the extraordinary circumstances possible so that the program will be robust
A platform is the hardware or software environment in which a program runs. Most platforms can be described as a combination of the operating system and hardware, like Windows 2000/XP, Linux, Solaris, and MacOS.
What is the main difference between Java platform and other platforms?
The Java platform differs from most other platforms in that it's a software-only platform that runs on top of other hardware-based platforms.
The Java platform has two components:
The Java Virtual Machine (Java VM)
The Java Application Programming Interface (Java API)
What is the Java Virtual Machine?
The Java Virtual Machine is a software that can be ported onto various hardware-based platforms.
What is the Java API?
The Java API is a large collection of ready-made software components that provide many useful capabilities, such as graphical user interface (GUI) widgets.
What is the package?
The package is a Java namespace or part of Java libraries. The Java API is grouped into libraries of related classes and interfaces; these libraries are known as packages.
What is native code?
The native code is code that after you compile it, the compiled code runs on a specific hardware platform.
Is Java code slower than native code?
Not really. As a platform-independent environment, the Java platform can be a bit slower than native code. However, smart compilers, well-tuned interpreters, and just-in-time bytecode compilers can bring performance close to that of native code without threatening portability.
What is the serialization?
The serialization is a kind of mechanism that makes a class or a bean persistence by having its properties or fields and state information saved and restored to and from storage.
How to make a class or a bean serializable?
By implementing either the java.io.Serializable interface, or the java.io.Externalizable interface. As long as one class in a class's inheritance hierarchy implements Serializable or Externalizable, that class is serializable.
How many methods in the Serializable interface?
There is no method in the Serializable interface. The Serializable interface acts as a marker, telling the object serialization tools that your class is serializable.
How many methods in the Externalizable interface?
There are two methods in the Externalizable interface. You have to implement these two methods in order to make your class externalizable. These two methods are readExternal() and writeExternal().
What is the difference between Serializalble and Externalizable interface?
When you use Serializable interface, your class is serialized automatically by default. But you can override writeObject() and readObject() two methods to control more complex object serailization process. When you use Externalizable interface, you have a complete control over your class's serialization process.
What is a transient variable?
A transient variable is a variable that may not be serialized. If you don't want some field not to be serialized, you can mark that field transient or static.
Which containers use a border layout as their default layout?
The window, Frame and Dialog classes use a border layout as their default layout.
How are Observer and Observable used?
Objects that subclass the Observable class maintain a list of observers. When an Observable object is updated it invokes the update() method of each of its observers to notify the observers that it has changed state. The Observer interface is implemented by objects that observe Observable objects.
What are synchronized methods and synchronized statements?
Synchronized methods are methods that are used to control access to an object. A thread only executes a synchronized method after it has acquired the lock for the method's object or class. Synchronized statements are similar to synchronized methods. A synchronized statement can only be executed after a thread has acquired the lock for the object or class referenced in the synchronized statement.
What are three ways in which a thread can enter the waiting state?
A thread can enter the waiting state by invoking its sleep() method, by blocking on I/O, by unsuccessfully attempting to acquire an object's lock, or by invoking an object's wait() method. It can also enter the waiting state by invoking its (deprecated) suspend() method.
Can a lock be acquired on a class?
Yes, a lock can be acquired on a class. This lock is acquired on the class's Class object.
What's new with the stop(), suspend() and resume() methods in JDK 1.2?
The stop(), suspend() and resume() methods have been deprecated in JDK 1.2.
What is the preferred size of a component?
The preferred size of a component is the minimum component size that will allow the component to display normally.
What method is used to specify a container's layout?
The setLayout() method is used to specify a container's layout.
Which containers use a FlowLayout as their default layout?
The Panel and Applet classes use the FlowLayout as their default layout.
What state does a thread enter when it terminates its processing?
When a thread terminates its processing, it enters the dead state.
What is the Collections API?
The Collections API is a set of classes and interfaces that support operations on collections of objects.
What is the List interface?
The List interface provides support for ordered collections of objects.
How does Java handle integer overflows and underflows?
It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.
What is the Vector class?
The Vector class provides the capability to implement a growable array of objects
What modifiers may be used with an inner class that is a member of an outer class?
A (non-local) inner class may be declared as public, protected, private, static, final, or abstract.
If a method is declared as protected, where may the method be accessed?
A protected method may only be accessed by classes or interfaces of the same package or by subclasses of the class in which it is declared.
What is an Iterator interface?
The Iterator interface is used to step through the elements of a Collection.
How many bits are used to represent Unicode, ASCII, UTF-16, and UTF-8 characters?
Unicode requires 16 bits and ASCII require 7 bits. Although the ASCII character set uses only 7 bits, it is usually represented as 8 bits. UTF-8 represents characters using 8, 16, and 18 bit patterns. UTF-16 uses 16-bit and larger bit patterns.
What is the difference between yielding and sleeping?
When a task invokes its yield() method, it returns to the ready state. When a task invokes its sleep() method, it returns to the waiting state.
Is sizeof a keyword?
The sizeof operator is not a keyword.
What are wrapped classes?
Wrapped classes are classes that allow primitive types to be accessed as objects.
Does garbage collection guarantee that a program will not run out of memory?
No, it doesn't. It is possible for programs to use up memory resources faster than they are garbage collected. It is also possible for programs to create objects that are not subject to garbage collection
What is the difference between preemptive scheduling and time slicing?
Under preemptive scheduling, the highest priority task executes until it enters the waiting or dead states or a higher priority task comes into existence. Under time slicing, a task executes for a predefined slice of time and then reenters the pool of ready tasks. The scheduler then determines which task should execute next, based on priority and other factors.
Name Component subclasses that support painting.
The Canvas, Frame, Panel, and Applet classes support painting.
What is a native method?
A native method is a method that is implemented in a language other than Java.
How can you write a loop indefinitely?
for(;;)--for loop; while(true)--always true, etc.
Can an anonymous class be declared as implementing an interface and extending a class?
An anonymous class may implement an interface or extend a superclass, but may not be declared to do both.
What is the purpose of finalization?
The purpose of finalization is to give an unreachable object the opportunity to perform any cleanup processing before the object is garbage collected.
Which class is the superclass for every class.
Object
What invokes a thread's run() method?
After a thread is started, via its start() method or that of the Thread class, the JVM invokes the thread's run() method when the thread is initially executed.
What is the difference between the Boolean & operator and the && operator?
If an expression involving the Boolean & operator is evaluated, both operands are evaluated. Then the & operator is applied to the operand. When an expression involving the && operator is evaluated, the first operand is evaluated. If the first operand returns a value of true then the second operand is evaluated. The && operator is then applied to the first and second operands. If the first operand evaluates to false, the evaluation of the second operand is skipped.
Operator & has no chance to skip both sides evaluation and && operator does. If asked why, give details as above.
What is the GregorianCalendar class?
The GregorianCalendar provides support for traditional Western calendars.
What is the SimpleTimeZone class?
The SimpleTimeZone class provides support for a Gregorian calendar.
Which Container method is used to cause a container to be laid out and redisplayed?
validate()
What is the Properties class?
The properties class is a subclass of Hashtable that can be read from or written to a stream. It also provides the capability to specify a set of default values to be used.
What is the purpose of the Runtime class?
The purpose of the Runtime class is to provide access to the Java runtime system.
What is the purpose of the System class?
The purpose of the System class is to provide access to system resources.
What is the purpose of the finally clause of a try-catch-finally statement?
The finally clause is used to provide the capability to execute code no matter whether or not an exception is thrown or caught.
What is the Locale class?
The Locale class is used to tailor program output to the conventions of a particular geographic, political, or cultural region.
What must a class do to implement an interface?
It must provide all of the methods in the interface and identify the interface in its implements clause.
What is the purpose of the wait(), notify(), and notifyAll() methods?
The wait(),notify(), and notifyAll() methods are used to provide an efficient way for threads to communicate each other.
What is an abstract method?
An abstract method is a method whose implementation is deferred to a subclass. Or, a method that has no implementation (an interface of a method).
What is a static method?
A static method is a method that belongs to the class rather than any object of the class and doesn't apply to an object or even require that any objects of the class have been instantiated
What is a protected method?
A protected method is a method that can be accessed by any method in its package and inherited by any subclass of its class.
What are the high-level thread states?
The high-level thread states are ready, running, waiting, and dead.
What is the difference between a static and a non-static inner class?
A non-static inner class may have object instances that are associated with instances of the class's outer class. A static inner class does not have any object instances.
What is an object's lock and which object's have locks?
An object's lock is a mechanism that is used by multiple threads to obtain synchronized access to the object. A thread may execute a synchronized method of an object only after it has acquired the object's lock. All objects and classes have locks. A class's lock is acquired on the class's Class object.
When can an object reference be cast to an interface reference?
An object reference be cast to an interface reference when the object implements the referenced interface.
What is the difference between a Window and a Frame?
The Frame class extends Window to define a main application window that can have a menu bar.
What do heavy weight components mean?
Heavy weight components like Abstract Window Toolkit (AWT), depend on the local windowing toolkit. For example, java.awt.Button is a heavy weight component, when it is running on the Java platform for Unix platform, it maps to a real Motif button. In this relationship, the Motif button is called the peer to the java.awt.Button. If you create two Buttons, two peers and hence two Motif Buttons are also created. The Java platform communicates with the Motif Buttons using the Java Native Interface. For each and every component added to the application, there is an additional overhead tied to the local windowing system, which is why these components are called heavy weight.
Which package has light weight components?
javax.Swing package. All components in Swing, except JApplet, JDialog, JFrame and JWindow are lightweight components.
What are peerless components?
The peerless components are called light weight components.
What is the difference between the Font and FontMetrics classes?
The FontMetrics class is used to define implementation-specific properties, such as ascent and descent, of a Font object.
What happens when a thread cannot acquire a lock on an object?
If a thread attempts to execute a synchronized method or synchronized statement and is unable to acquire an object's lock, it enters the waiting state until the lock becomes available.
What is the difference between the Reader/Writer class hierarchy and the InputStream/OutputStream class hierarchy?
The Reader/Writer class hierarchy is character-oriented, and the InputStream/OutputStream class hierarchy is byte-oriented.
What classes of exceptions may be caught by a catch clause?
A catch clause can catch any exception that may be assigned to the Throwable type. This includes the Error and Exception types.
What is the difference between throw and throws keywords?
The throw keyword denotes a statement that causes an exception to be initiated. It takes the Exception object to be thrown as argument. The exception will be caught by an immediately encompassing try-catch construction or propagated further up the calling hierarchy.
The throws keyword is a modifier of a method that designates that exceptions may come out of the method, either by virtue of the method throwing the exception itself or because it fails to catch such exceptions that a method it calls may throw.
If a class is declared without any access modifiers, where may the class be accessed?
A class that is declared without any access modifiers is said to have package or friendly access. This means that the class can only be accessed by other classes and interfaces that are defined within the same package.
What is the Map interface?
The Map interface replaces the JDK 1.1 Dictionary class and is used associate keys with values.
Does a class inherit the constructors of its superclass?
A class does not inherit constructors from any of its superclasses.
Name primitive Java types.
The primitive types are byte, char, short, int, long, float, double, and boolean.
Which class should you use to obtain design information about an object?
The Class class is used to obtain information about an object's design.
How can a GUI component handle its own events?
A component can handle its own events by implementing the required event-listener interface and adding itself as its own event listener.
How are the elements of a GridBagLayout organized?
The elements of a GridBagLayout are organized according to a grid. However, the elements are of different sizes and may occupy more than one row or column of the grid. In addition, the rows and columns may have different sizes.
What advantage do Java's layout managers provide over traditional windowing systems?
Java uses layout managers to lay out components in a consistent manner across all windowing platforms. Since Java's layout managers aren't tied to absolute sizing and positioning, they are able to accommodate platform-specific differences among windowing systems.
What are the problems faced by Java programmers who don't use layout managers?
Without layout managers, Java programmers are faced with determining how their GUI will be displayed across multiple windowing systems and finding a common sizing and positioning that will work within the constraints imposed by each windowing system.
What is the difference between static and non-static variables?
A static variable is associated with the class as a whole rather than with specific instances of a class. Non-static variables take on unique values with each object instance.
What is the difference between the paint() and repaint() methods?
The paint() method supports painting via a Graphics object. The repaint() method is used to cause paint() to be invoked by the AWT painting thread.
What is the purpose of the File class?
The File class is used to create objects that provide access to the files and directories of a local file system.
How does multithreading take place on a computer with a single CPU?
The operating system's task scheduler allocates execution time to multiple tasks. By quickly switching between executing tasks, it creates the impression that tasks execute sequentially.
What restrictions are placed on method overloading?
Two methods may not have the same name and argument list but different return types.
What restrictions are placed on method overriding?
Overridden methods must have the same name, argument list, and return type. The overriding method may not limit the access of the method it overrides. The overriding method may not throw any exceptions that may not be thrown by the overridden method.
What is casting?
There are two types of casting, casting between primitive numeric types and casting between object references. Casting between numeric types is used to convert larger values, such as double values, to smaller values, such as byte values. Casting between object references is used to refer to an object by a compatible class, interface, or array type reference
Name Container classes. ?
Window, Frame, Dialog, FileDialog, Panel, Applet, or ScrollPane
What class allows you to read objects directly from a stream?
The ObjectInputStream class supports the reading of objects from input streams.
How are this() and super() used with constructors?
this() is used to invoke a constructor of the same class. super() is used to invoke a superclass constructor.
How is it possible for two String objects with identical values not to be equal under the == operator?
The == operator compares two objects to determine if they are the same object in memory. It is possible for two String objects to have the same value, but located indifferent areas of memory.
What an I/O filter?
An I/O filter is an object that reads from one stream and writes to another, usually altering the data in some way as it is passed from one stream to another.
What is the Set interface?
The Set interface provides methods for accessing the elements of a finite mathematical set. Sets do not allow duplicate elements.
What is the List interface?
The List interface provides support for ordered collections of objects.
What is the purpose of the enableEvents() method?
The enableEvents() method is used to enable an event for a particular object. Normally, an event is enabled when a listener is added to an object for a particular event. The enableEvents() method is used by objects that handle events by overriding their event-dispatch methods.
What is the difference between the File and RandomAccessFile classes?
The File class encapsulates the files and directories of the local file system. The RandomAccessFile class provides the methods needed to directly access data contained in any part of a file.
What interface must an object implement before it can be written to a stream as an object?
An object must implement the Serializable or Externalizable interface before it can be written to a stream as an object.
What is the ResourceBundle class?
The ResourceBundle class is used to store locale-specific resources that can be loaded by a program to tailor the program's appearance to the particular locale in which it is being run.
What is the difference between a Scrollbar and a ScrollPane?
A Scrollbar is a Component, but not a Container. A ScrollPane is a Container. A ScrollPane handles its own events and performs its own scrolling.
What is a Java package and how is it used?
A Java package is a naming context for classes and interfaces. A package is used to create a separate name space for groups of classes and interfaces. Packages are also used to organize related classes and interfaces into a single API unit and to control accessibility to these classes and interfaces.
What are the Object and Class classes used for?
The Object class is the highest-level class in the Java class hierarchy. The Class class is used to represent the classes and interfaces that are loaded by a Java program.
What is Serialization and deserialization?
Serialization is the process of writing the state of an object to a byte stream.
Deserialization is the process of restoring these objects.
What is tunnelling?
Tunnelling is a route to somewhere. For example, RMI tunnelling is a way to make RMI application get through firewall. In CS world, tunnelling means a way to transfer data.
Does the code in finally block get executed if there is an exception and a return statement in a catch block?
If an exception occurs and there is a return statement in catch block, the finally block is still executed. The finally block will not be executed when the System.exit(1) statement is executed earlier or the system shut down earlier or the memory is used up earlier before the thread goes to finally block.
How you restrict a user to cut and paste from the html page?
Using javaScript to lock keyboard keys. It is one of solutions.
Is Java a super set of JavaScript?
No. They are completely different. Some syntax may be similar.
What is a Container in a GUI?
A Container contains and arranges other components (including other containers) through the use of layout managers, which use specific layout policies to determine where components should go as a function of the size of the container.
How the object oriented approach helps us keep complexity of software development under control?
We can discuss such issue from the following aspects:
Objects allow procedures to be encapsulated with their data to reduce potential interference.
Inheritance allows well-tested procedures to be reused and enables changes to make once and have effect in all relevant places.
The well-defined separations of interface and implementation allows constraints to be imposed on inheriting classes while still allowing the flexibility of overriding and overloading.
What is polymorphism?
Polymorphism allows methods to be written that needn't be concerned about the specifics of the objects they will be applied to. That is, the method can be specified at a higher level of abstraction and can be counted on to work even on objects of yet unconceived classes.
What is design by contract?
The design by contract specifies the obligations of a method to any other methods that may use its services and also theirs to it. For example, the preconditions specify what the method required to be true when the method is called. Hence making sure that preconditions are. Similarly, post conditions specify what must be true when the method is finished, thus the called method has the responsibility of satisfying the post conditions.
In Java, the exception handling facilities support the use of design by contract, especially in the case of checked exceptions. The assert keyword can be used to make such contracts.
What are use cases?
A use case describes a situation that a program might encounter and what behavior the program should exhibit in that circumstance. It is part of the analysis of a program. The collection of use cases should, ideally, anticipate all the standard circumstances and many of the extraordinary circumstances possible so that the program will be robust
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