HOME      BLOG       FORUMS      CONTACT       ABOUT

Core Java interview questions – Part 6

March 18th, 2012 Albin Joseph Posted in Core Java interview questions | 11 Comments »

91. What is java byte code?
Byte code is an sort of intermediate code. The byte code is processed by virtual machine.

92. What is method overloading?
Method overloading is the process of creating a new method with the same name and different signature.

93. What is method overriding?
Method overriding is the process of giving a new definition for an existing method in its child class.
Read the rest of this entry »

Tags: , , ,

AddThis Social Bookmark Button

Core Java interview questions – Part 7

March 15th, 2012 Albin Joseph Posted in Core Java interview questions | 1 Comment »

106. What is java collections?
Java collections is a set of classes, that allows operations on a collection of classes.

107. Can we compile a java program without main?
Yes, we can. In order to compile a java program, we don’t require any main method. But to execute a java program we must have a main in it (unless it is an applet or servlet). Because main is the starting point of a java program.
Read the rest of this entry »

Tags: , , ,

AddThis Social Bookmark Button

Core Java interview questions – Part 8

March 7th, 2012 Albin Joseph Posted in Core Java interview questions | No Comments »

121. What is an interface?
An interface is a collection of method declarations and constants. In java interfaces are used to achieve multiple inheritance. It sets a behavioral protocol to all implementing classes.

122. What is an abstract class?
An abstract class is an incomplete class. An abstract class is defined with the keyword abstract . We cannot create an object of the abstract class because it is not complete. It sets a behavioral protocol for all its child classes.
Read the rest of this entry »

Tags: , , ,

AddThis Social Bookmark Button

Core Java interview questions – Part 9

March 6th, 2012 Albin Joseph Posted in Core Java interview questions | No Comments »

136. Why Java is not 100% pure object oriented language?
Because java uses primitives.

137. Why ArrayList is faster than Vector?
Because Vector is synchronized. Synchronization reduces the performance.

138. What is the security mechanism used in java?
Java uses sand box security model.
Read the rest of this entry »

Tags: , , ,

AddThis Social Bookmark Button

Core Java interview questions – Part 10

February 20th, 2012 Albin Joseph Posted in Core Java interview questions | No Comments »

151. What is meant by Open Source ?
In general, open source refers to any program whose source code is made available for use or modification as users or other developers see fit. Open source software is usually developed as a public collaboration and made freely available.

152. How do you send data from an applet to Servlet ? What are the steps involved in it ?
You can use the java.net.URLConnection and java.net.URL classes to open a standard HTTP connection to the web server. The server then passes this information to the servlet in the normal way.

Basically, the applet pretends to be a web browser, and the servlet doesn’t know the difference. As far as the servlet is concerned, the applet is just another HTTP client.
Read the rest of this entry »

Tags: , , ,

AddThis Social Bookmark Button

Core Java interview questions – Part 11

February 12th, 2012 Albin Joseph Posted in Core Java interview questions | No Comments »

166. What is aggregation?
It is a special type of composition. If you expose all the methods of a composite class and route the method call to the composite method through its reference, then it is called aggregation

167. What are the different methods available in Object?
clone, equals, wait, finalize, getClass, hashCode, notify, notifyAll, toString
Read the rest of this entry »

Tags: , , ,

AddThis Social Bookmark Button

Core Java interview questions – Part 12

February 7th, 2012 Albin Joseph Posted in Core Java interview questions | No Comments »

181. What is an Object and how do you allocate memory to it?
Object is an instance of a class and it is a software unit that combines a structured set of data with a set of operations for inspecting and manipulating that data. When an object is created using new operator, memory is allocated to it.

182. What is UNICODE?
Unicode is used for internal representation of characters and strings and it uses 16 bits to represent each other.
Read the rest of this entry »

Tags: , , ,

AddThis Social Bookmark Button

JSP/Servlets interview questions

January 20th, 2012 Albin Joseph Posted in JSP/Servlet interview questions | 14 Comments »

Here you can find out a list of interview questions for jsp and servlets. These questions are often asked by the interviewer for jsp interview and servlet interview. We put our maximum effort to make this answers error free. But still there might be some errors. If you feel out any answer given for any question is wrong, please, please inform us by clicking on report bug button provided below.

In this section we are offering interview questions for JSP and Servlets only. Since JSP and Servlets are almost identical technology, there is only one section for both JSP and Servlet interview questions. If you need interview questions for any other java related technologies , please check the relevant sections.
Read the rest of this entry »

Tags: , , ,

AddThis Social Bookmark Button

JSP/Servlets interview questions – Part 1

September 7th, 2011 Albin Joseph Posted in JSP/Servlet interview questions | 10 Comments »

21. What are the implicit objects?
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 are: request, response, pageContext, session, application, out, config, page, exception

22. What’s the difference between forward and sendRedirect?
forward is server side redirect and sendRedirect is client side redirect. 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 completely with in the web container And then returns to the calling method. When a sendRedirect 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 completely 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. Client can disable sendRedirect.

23. What are the different scopes available ?
page, request, session, application

24. Is JSP extensible ?
Yes, it is. JSP technology is extensible through the development of custom actions, or tags, which are encapsulated in tag libraries.

25. What’s the Servlet Interface?
The central abstraction in the Servlet API is the Servlet interface. All servlets implement this interface, either directly or, more commonly, by extending a class that implements it such as HttpServlet.

26. What are two different types of Servlets ?
GenericServlet and HttpServlet. HttpServlet is used to implement HTTP protocol, where as Generic servlet can implement any protocol.

27. What is the life cycle of servlet?
Each servlet has the same life cycle: first, the server loads and initializes the servlet by calling the init method. This init() method will be executed only once during the life time of a servlet. Then when a client makes a request, it executes the service method. finally it executes the destroy() method when server removes the servlet.

28. Can we call destroy() method on servlets from service method ?
Yes.

29. What is the need of super.init (config) in servlets ?
Then only we will be able to access the ServletConfig from our servlet. If there is no ServletConfig our servlet will not have any servlet nature.

30. What is the difference between GenericServlet and HttpServlet?
GenericServlet supports any protocol. HttpServlet supports only HTTP protocol. By extending GenericServlet we can write a servlet that supports our own custom protocol or any other protocol.

32. Can we write a constructor for servlet ?
Yes. But the container will always call the default constructor only. If default constructor is not present , the container will throw an exception.

33. What is the difference between <%@ include ...> (directive include) and ?
@ include is static include. It is inline inclusion. The contents of the file will get included on Translation phase. It is something like inline inclusion. We cannot have a dynamic filename for directive include. is dynamic include. Here the included file will be processed as a separate file and the response will be included. We can have a dynamic filename for . We can also pass parameters to 34. Can I just abort processing a JSP?
Yes. You can put a return statement to abort JSP processing.

35. What are the parameters for service method ?
ServletRequest and ServletResponse

36. What are cookies ?
Cookies are small textual information that are stored on client computer. Cookies are used for session tracking.

37. How do I prevent the output of my JSP or Servlet pages from being cached by the browser?
By setting appropriate HTTP header attributes we can prevent caching by the browser

<%
response.setHeader("Cache-Control","no-store"); //HTTP 1.1
response.setHeader("Pragma","no-cache"); //HTTP 1.0
response.setDateHeader ("Expires", 0); //prevents caching at the proxy server
%>

38. How to refer the “this” variable within a JSP page?
Under JSP 1.0, the page implicit object page is equivalent to “this”, and returns a reference to the servlet generated by the JSP page.

39. How many JSP scripting elements and what are they?
There are three scripting elements in JSP . They are declarations, scriptlets, expressions.

40. Can we implement an interface in JSP ?
No.

Tags: , , ,

AddThis Social Bookmark Button

JSP/Servlets interview questions Part 2

September 4th, 2011 Albin Joseph Posted in JSP/Servlet interview questions | No Comments »

40. What is the meaning of response has already been committed error?
You will get this error only when you try to redirect a page after you already have flushed the output buffer. This happens because HTTP specification force the header to be set up before the lay out of the page can be shown. When you try to send a redirect status, your HTTP server cannot send it right now if it hasn’t finished to set up the header. Simply it is giving the error due to the specification of HTTP 1.0 and 1.1

42. How do I use a scriptlet to initialize a newly instantiated bean?
A jsp:useBean action may optionally have a body. If the body is specified, its contents will be automatically invoked when the specified bean is instantiated (Only at the time of instantiation.) Typically, the body will contain scriptlets or jsp:setProperty tags to initialize the newly instantiated bean, although you are not restricted to using those alone.

43. What is JSP?
JSP is a server side scripting technology. JSP allows Java as well as a few special tags to be embedded into a web file (HTML/XML, etc). The suffix must ends with .jsp.

44. What are JSP Actions?
JSP actions use constructs in XML syntax to control the behavior of the servlet engine. You can dynamically insert a file, reuse JavaBeans components, forward the user to another page, or generate HTML for the Java plugin. Available actions include: jsp:include, jsp:useBean, jsp:setProperty, jsp:getProperty, jsp:forward and Jsp: plugin

45. What is the difference between ServletContext and ServletConfig?
The ServletConfig gives the information about the servlet initialization parameters. The servlet engine implements the ServletConfig interface in order to pass configuration information to a servlet. The server passes an object that implements the ServletConfig interface to the servlet’s init() method. The ServletContext gives information about the container. The ServletContext interface provides information to servlets regarding the environment in which they are running. It also provides standard way for servlets to write events to a log file.

46. How can a servlet refresh automatically?
We can use a client-side Refresh or Server Push

47. What is Server side push?
Server Side push is useful when data needs to change regularly on the clients application or browser, without intervention from client. The mechanism used is, when client first connects to Server, then Server keeps the TCP/IP connection open.

48. What is client side refresh?
The standard HTTP protocols ways of refreshing the page, which is normally supported by all browsers.

<META HTTP-EQUIV="Refresh" CONTENT="5; URL=/servlet/MyServlet/">

This will refresh the page in the browser automatically and loads the new data every 5 seconds.

49. What is the Max amount of information that can be saved in a Session Object ?
There is no such limit on the amount of information that can be saved in a Session Object. The only limit is the Session ID length , which should not exceed more than 4K.

50. Why should we go for inter servlet communication?
The three major reasons to use inter servlet communication are: a) Direct servlet manipulation – allows to gain access to the other currently loaded servlets and perform certain tasks (through the ServletContext object) b) Servlet reuse – allows the servlet to reuse the public methods of another servlet. c) Servlet collaboration – requires to communicate with each other by sharing specific information (through method invocation)

51. What is a output comment?
A comment that is sent to the client in the viewable page source. The JSP engine handles an output comment as un interpreted HTML text, returning the comment in the HTML output sent to the client. You can see the comment by viewing the page source from your Web browser.

52. What is a Hidden Comment
Hidden Comments are JSP comments. A comments that documents the JSP page but is not sent to the client. The JSP engine ignores a hidden comment, and does not process any code within hidden comment tags.

53. What are the differences between a session and a cookie?
Session is stored in server but cookie stored in client. Session should work regardless of the settings on the client browser. There is no limit on the amount of data that can be stored on session. But it is limited in cookie. Session can store objects and cookies can store only strings. Cookies are faster than session.

54. What is HttpTunneling?
HTTP tunneling is used to encapsulate other protocols within the HTTP or HTTPS protocols. Normally the intranet is blocked by a firewall and the network is exposed to the outer world only through a specific web server port, that listens for only HTTP requests. To use any other protocol, that by passes the firewall, the protocol is embedded in HTTP and send as HttpRequest.

55. How to pass information from JSP to included JSP?
By using tag.

56. What is the better way to enable thread-safe servlets and JSPs? SingleThreadModel Synchronization?
The better approach is to use synchronization. Because SingleThreadModel is not scalable. SingleThreadModel is pretty resource intensive from web server’s perspective. The most serious issue is when the number of concurrent requests exhaust the servlet instance pool. In that case, all the un serviced requests are queued until something becomes free – which results in poor performance.

57. What is the difference between ServletContext and PageContext?
ServletContext gives the information about the container and PageContext gives the information about the Request

58. Why in Servlet 2.4 specification SingleThreadModel has been deprecated?
SingleThreadModel is pretty resource intensive from web server’s perspective. When the number of concurrent requests exhaust the servlet instance pool, all the un serviced requests are queued until something becomes free – which results in poor performance.

59. How do you pass data (including JavaBeans) to a JSP from a servlet?
By forwarding the request to the servlet ( the data must be there in the request scope) we can pass the data from a JSP to servlet. Also we can use a session to pass the data.

60. How can I set a cookie?

	Cookie c = new Cookie("name","value");
    response.addCookie(c);

Tags: , , ,

AddThis Social Bookmark Button