What are ear, war and jar files? What are J2EE Deployment Descriptors?

ear, war and jar are standard application deployment archive files. Since they are a standard, any application server will know how to unpack and deploy them.

An EAR file is a standard JAR file with an ".ear" extension, named from Enterprise Archive file.

What is the catch or declare rule for method declarations?

If a checked exception may be thrown within the body of a method, the method must either catch the exception or declare it in its throws clause.

What are order of precedence and associativity, and how are they used?

Order of precedence determines the order in which operators are evaluated in expressions. Associatity determines whether an expression is evaluated left-to-right or right-to-left

What is a native method?

A native method is a method that is implemented in a language other than Java.

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.

What restrictions are placed on the location of a package statement within a source code file?

A package statement must appear as the first line in a source code file (excluding blank lines and comments).

Does garbage collection guarantee that a program will not run out of memory?

Garbage collection does not guarantee that a program will not run out of memory. 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 are wrapped classes?

Wrapped classes are classes that allow primitive types to be accessed as objects.

Which java.util classes and interfaces support event handling?

The EventObject class and the EventListener interface support event processing.

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.

What are the implicit services provide by an EJB container?

Lifecycle Management: Individual enterprise beans do not need to explicitly manage process allocation,
thread management, object activation, or object destruction.

How does an EJB interact with its container and what are the call-back methods in entity beans?

EJB interacts with its container through the following mechanisms

Call-back Methods: Every EJB implements an interface (extends EnterpriseBean) which defines several
methods which alert the bean to various events in its lifecycle.

Can an EJB client invoke a method on a bean directly?

An EJB client should never access an EJB directly. Any access is done through the container. The container will intercept the client call and apply services like transaction, security etc prior to invoking the actual EJB. This relationship between the EJB and the container is like "don't call us, we will call you".

What are the different kinds of enterprise beans?

Session Bean: is a non-persistent object that implements some business logic running on the server. Session beans do not survive system shut down.

What are the benefits of Clustering and workload management?

1. It balances client processing requests, allowing incoming work requests to be distributed according to a configured Workload Management selection policy.

What is the difference between Message Driven Beans and Stateless Session beans?

In several ways, the dynamic creation and allocation of message-driven bean instances mimics the behavior of stateless session EJB instances, which exist only for the duration of a particular method call.

What are the basic classes required in the client for invoking an EJB?

The home and the remote interfaces, the implementation of the Naming Context Factory, the stubs and skeletons. In some App servers the stubs and the skeletons can be dynamically downloaded from the server

What is the new basic requirement for a CMP entity bean class in 2.0 from that of ejb 1.1?

must be abstract class. The container extends it and implements methods which are required for managing the relationships

How does a container-managed relationship work?

An entity bean accesses related entity beans by means of the accessor methods for its container-managed relationship fields, which are specified by the cmr-field elements of its abstract persistence schema defined in the deployment descriptor.

Explain declarative security for WEB applications?

Servlet containers implement declarative security. The administration is done through the deployment descriptor web.xml file.

What is a filter, and how does it work?

A filter dynamically intercepts requests and responses to transform or use the information contained in the requests or responses but typically do not themselves create responses. Filters can also be used to transform the response from the Servlet or JSP before sending it back to client.

What are the main elements of JSP? What are scriplets? What are expressions?

There are two types of data in a JSP page.

1. Static part (ie HTML, CSS etc), which gets copied directly to the response by the JSP Engine.
2. Dynamic part, which contains anything that can be translated and compiled by the JSP Engine.

What is a filter, and how does it work?

A filter dynamically intercepts requests and responses to transform or use the information contained in the requests or responses but typically do not themselves create responses. Filters can also be used to transform the response from the Servlet or JSP before sending it back to client.

What is the difference between forwarding a request and redirecting a request?

REDIRECT:
Sends a header back to the browser, which contains the name of he resource to be redirected to. The browser will make a fresh equest from this header information. Need to provide absolute URL path.

Explain the life cycle methods of a JSP?

• JSPs Pre-translated: Before the JSP file has been translated and compiled into the Servlet.
• JSPs Translated: The JSP file has been translated and compiled as a Servlet.
• Initialized: Prior to handling the requests in the service method the container calls the jspInit() to initialize the Servlet.

What is a JSP? What is it used for? What do you understand by the term JSP translation phase or compilation

JSP (Java ServerPages) is an extension of the Java Servlet technology. JSP is commonly used as the presentation layer for combining HTML and Java code. While Java Servlet technology is capable of generating HTML with out.println(“….. ”) statements, where out is a PrintWriter.