Interview FAQ's In JAVA - Part I

[sivaji]

Interview FAQ's In JAVA

Q: What is an enumeration?

A: An enumeration is an interface containing methods for accessing the underlying data structure from which the enumeration
     is obtained. It is a construct which collection classes return when you request a collection of all the objects stored in the
     collection. It allows sequential access to all the elements stored in the collection.

Q: Considering the basic properties of Vector and ArrayList, where will you use Vector and where will you use ArrayList?
A: The basic difference between a Vector and an ArrayList is that, vector is synchronized while ArrayList is not. Thus
     whenever there is a possibility of multiple threads accessing the same instance, one should use Vector. While if not 
     multiple threads are going to access the same instance then use ArrayList. Non synchronized data structure will give
     better performance than the synchronized one.

Q: Can a vector contain heterogenous objects?

A: Yes a Vector

Q: What is a Scriptlet?

A: A scriptlet can contain any number of language statements, variable or method declarations, or expressions that are valid
    in the page scripting language.Within scriptlet tags, you can
    1.Declare variables or methods to use later in the file (see also Declaration).
    2.Write expressions valid in the page scripting language (see also _Expression).
    3.Use any of the JSP implicit objects or any object declared with a <jsp:useBean> tag.
    You must write plain text, HTML-encoded text, or other JSP tags outside the scriptlet.
    Scriptlets are executed at request time, when the JSP engine processes the client request. If the scriptlet produces output,
    the output is stored in the out object, from which you can display it.

Q: What are implicit objects? List them?
A: Certain objects that are available for the use in JSP documents without being declared first. These objects are parsed by
     the JSP engine and inserted into the generated servlet. The implicit objects re listed below
     * request
     * response
     * pageContext
     * session
     * application
     * out
     * config
     * page
     * exception

Q: Difference between forward and sendRedirect?

A: When you invoke a forward request, the request is sent to another resource on the server, without the client being
     informed that a different resource is going to process the request. This process occurs completly with in the web
     container. When a sendRedirtect method is invoked, it causes the web container to return to the browser indicating that a
     new URL should be requested. Because the browser issues a completly new request any object that are stored as request
     attributes before the redirect occurs will be lost. This extra round trip a redirect is slower than forward.

Q: What are the different scope valiues for the <jsp:useBean>?

A: The different scope values for <jsp:useBean> are
     1. page
     2. request
     3.session
     4.application

Q: Explain the life-cycle mehtods in JSP?

A: THe generated servlet class for a JSP page implements the HttpJspPage interface of the javax.servlet.jsp package. Hte HttpJspPage interface extends the JspPage interface which inturn extends the Servlet interface of the javax.servlet package. the generated servlet class thus implements all the methods of the these three interfaces. The JspPage interface declares only two mehtods - jspInit() and jspDestroy() that must be implemented by all JSP pages regardless of the client-server protocol. However the JSP specification has provided the HttpJspPage interfaec specifically for the JSp pages serving HTTP requests. This interface declares one method _jspService().

The jspInit()- The container calls the jspInit() to initialize te servlet instance.It is called before any other method, and is called only once for a servlet instance.

The _jspservice()- The container calls the _jspservice() for each request, passing it the request and the response objects.

The jspDestroy()- The container calls this when it decides take the instance out of service. It is the last method called n the servlet instance.

Q: What are the different kinds of enterprise beans?

A: Different kind of enterrise beans are Stateless session bean, Stateful session bean, Entity bean, Message-driven bean.....

Q: What is Session Bean?

A: A session bean is a non-persistent object that implements some business logic running on the server. One way to think of
     a session object...........

Q: What is Entity Bean?

A: The entity bean is used to represent data in the database. It provides an object-oriented interface to ...........

Q: What are the methods of Entity Bean?
A: An entity bean consists of 4 groups of methods, create methods...........

Q: What is the difference between Container-Managed Persistent (CMP) bean and Bean-Managed Persistent(BMP) ?

A: Container-managed persistence (CMP) and bean-managed persistence (BMP). With CMP, the container manages the
     persistence of the entity bean............

Q: What are the callback methods in Entity beans?

A: Callback methods allows the container to notify the bean of events in its life cycle. The callback methods are defined in the
     javax.ejb.EntityBean interface............

Q: What is software architecture of EJB?

A: Session and Entity EJBs consist of 4 and 5 parts respectively, a remote interface...........