Java Interview Questions on Development

Interview questions on java development. In this article I have given solutions in programmatically and diagrammatically for each and every question.

Here the questions are how to compile and run java programs, how to compile multiple java source files etc.

1) What is the purpose of javac command?

We use javac command to compile a single or group of java source files.

Example:- (D:\Java)

class Test {

          public static void main(String[] args)    {

               System.out.println("Hello Test Class");

           }

} 

D:\Java>javac Test.java

We can compile multiple classes simultaneously.

D:\Java>javac One.java Two.java

Or

D:\Java>javac *.java

All java source files will be compile which are available in D:\Java 

Example:- (D:\Java)

package com.programmer;

class Test {

               public static void main(String[] args)   {

                               System.out.println("Hello Test Class");

               }

}

If a java program contain a package then we should compile as shown in the below.

D:\Java>javac –d Test.java

After compile the above program that corresponding .class file will be generate in the following folder Structure.

D:\Java\com\programmer

2) What is the purpose of java command?

The purpose of java command is to execute .class file.

Example:- (D:\Java)

class Test {

          public static void main(String[] args)   {

               System.out.println("Hello Test Class");

           }

}

D:\Java>java [options] Test

Options (-version, -cp/-classpath, -ea/-esa/-da/-dsa, -D)

“Test” is name of the .class file.

D:\Java>java Test

Output:

Hello Test class

If the .class file in other directory then we can run as shown in the below.

C:\>java –cp D:/Java Test

Output:

Hello Test class

Or

C:\>java –classpath D:/Java Test

Output:

Hello Test class

If .class file contain in current directory then we use .(dot) instead of D:

D:\>java –cp ./Java Test

Output:

Hello Test class

In the above command Test.class file available in D:/Java folder.

Example:- (D:\Java)

package com.programmer;

class Test {

               public static void main(String[] args)   {

                               System.out.println("Hello Test Class");

               }

} 

D:\Java>java com.programmer Test

Output:

Hello Test class

We can run .class file from another directory as sown in the below. 

C:\>java –cp D:/Java com.programmer Test

Output:

Hello Test class

3) Is it possible to compile multiple classes simultaneously?

Yes, it is possible to compile multiple classes simultaneously. But we can run only single .class file at a time.

D:\Java>javac One.java Two.java

Or

D:\Java>javac *.java

4) What is the difference between path and class path?

Path and classpath are system level environment variables.

Path is used to define where the system can find the executable files (.exe) whereas classpath is used to specify the location of .class file.

Example of path:

If we want compile and execute a java program, we must required that corresponding files (java.exe and javac.exe). this files are available in the following location “C:\Program Files\Java\jdk1.8.0_31\bin” so we set this path in environment variables as path variable value. 

Example for CLASSPATH:

classpath describes the location where required .class files are available. By default JVM will search for required .class file in the current working directory.

C:\>java –classpath D:/Java Test

Output:

Hello Test class

In the above command Test.class file available in D:/Java, when we run that command JVM will search for Test.class file in the D:/Java location.

5) What are various ways to set classpath? And which approach is recommended?

There are 3 ways to set java classpath:
By using environment variable classpath:-

Go to MyComputer properties -> advanced tab -> environment variables -> new tab of user variable -> write path in variable name -> past the path of bin folder location in variable value -> click ok.

This way of set classpath is permanent.

By using set command at command prompt:-
Copy the location of .class file and open command prompt pest that location as shown in the below.

C:\>set classpath=D:/Java

C:\>java Test

Output:

Hello Test Class

This way of setting classpath is available only for the current command prompt. Once we close command prompt we will be lost the classpath.
By using –cp/-classpath option at command level:-
By using –cp/-classpath option we set classpath at command level. Once command execute we lost classpath again we set and execute
Among 3 ways this is approach is recommended because dependent classes are varied from command to command. 

C:\>java -classpath D:/Java Test

Output:

Hello Test Class

6) Consider the command java –cp C:;D:;E: if the required .class file is available in C:, D:, E: location then which class file will be considered?

If we have Test.class file in C:, D: and E: directories then  if we use command as following in the below.

E:\>java -cp D:;. Test

D directory Test Class

In the above command first JVM search for Test.class file in D: location if it is available in D: then 

execute otherwise search in next directory .(dot mean current working directory E:).

E:\>java -cp .;D: Test

E directory Test Class

In the above command first JVM search for Test.class file in E: directory .(dot mean current working

directory E:) if it is not available in E: then search in D: location if it is available in D: then execute.

7) What is the purpose of jar file?

A Jar file contains mostly .class files and optionally other files like sound files, image files for Java applications, gathered into a single file in the compressed format.

If we grouped all those .class files into a zip file then we can make that zip file available in classpath. No need to set classpath individually to each and every .class file.

Example:- to write JDBC based application all dependent classes are available in “OJDBC14.jar” , we have to place this jar file in classpath then only our JDBC program will be compile and run.

8) Explain the process of creation and extraction of jar file?

Create a JAR file

Syntax: jar [options] file_names

Various options to create a JAR file

jar –cvf calculator.jar A.class

jar –cvf calculator.jar A.class B.class

jar –cvf calculator.jar *.class

jar –cvf calculator.jar *.*

c mean create.

v mean verbose output.

f mean filename.

Calculator is jar file name, here .class files are grouped into calculator.jar file.

Manifest file contain the .class file name which class contain main method.

Example:-

Creation and execution of jar file

D:\Java>jar –cvfm testjar.jar manifest.MF Test.class Test$1.class

D:\Java>java –jar testjar.jar

View contents of a JAR file

Syntax: jar tf jar_file_name

Example: D:\Java>jar tf Demo.jar

View contents with detail of a JAR file

Syntax: jar tvf jar_file_name

Example: 

D:\Java>jar tvf Demo.jar

Executing a JAR file

Syntax: java -jar jar_file_name

Example:

D:\Java>java –jar Demo.jar

9) How many ways we can run java program?       

We can run a java program in the following 4 ways.

1. From command prompt we can run .class file with “java” command.

2. From command prompt we can run .jar file with “java” command.

3. By double clicking a jar file.

4. By double clicking a batch file.

Batch file:- batch file contains commands, what command we want to execute we can write that command in a notepad and save it as abc.bat (with .bat extension) and execute it in command prompt

Example:-“java Test” save this in abc.bat file and open command prompt execute it

D:\Java>abc   then Test.class file will be executes.

10) What is the difference between jar,war,ear?

There are no structural differences between the files; they are all archived using zip/jar compression. However, they are intended for different purposes.

Jar files (java archive):-

A jar file contains a group of .class files. The extension of jar file is .jar.

Example of jar creation:-

jar –cvf calculator.jar *.class

  

War files (web archive):-

A war file represents a web application which contains servlets, jsp, HTML, CSS etc.

The main advantage of maintaining web application in the form of “war” file is project delivery, project transportation and project deployment will become easy.

Example of war creation:-

jar –cvf mywebapp.war *.*

Ear files (enterprise archive):-

An “ear” file represents an enterprise application which contains jsp, servlet, Ejb, jms components etc.

In general “ear file contain several “war and jar” file.

Example of ear creation:-

jar –cvf myapp.ear *.*

11) What is the difference between jdk,jre,jvm?

JVM

JVM stands for Java Virtual Machine, it is an interpreter which provides the runtime environment in which java byte code can be executed line by line.

JVMs are available for many hardware and software platforms (so JVM is platform dependent).

JRE

JRE stands for Java Runtime Environment to run java application. It is the implementation of JVM and physically exists. It contains JVM+set of library file (like .jar files) and other files.

JDK 

JDK stands for Java Development Kit to develop and run java applications. It is physically exists. It contains JRE + development tools(like java, javac etc.).

12) Explain about system properties and write program to display all system properties?

For every system some persistence information will be maintain in the form of system properties. This many include OS name, Java version, JVM vendor etc.

Program to display system properties:

import java.util.*;

class Test

{

               public static void main(String[] args)

               {

                               Properties p=System.getProperties();

                               p.list(System.out);

               }

}

13) How to set system properties from command prompt?

We can set system properties from the command prompt by using “-D” option

D:\Java>java –Dprogrammer=developer Test

-D means to set system property, Programmer mean property name, and Developer mean property value.

The main advantage of setting system property is we can customize behavior of java program.

14) What is Web application and Enterprise application?

A web application can be developed by only web related technologies like servlet, jsp, HML, CSS etc.

Example:- library management system

An enterprise application can be developed by any technology from java/j2ee like servlet, jsp ,ejb, jms components etc.

Example:- banking application telecom based applications

15) What are the web server and enterprise server?

Web server provides environment to run web application. Web server provides support only for web applications.

Web servers:- tomcat, oracle HTTP Server.

Application server provides environment to run enterprise application. Application server can provides support for any technologies like web applications and enterprise applications.

Application servers:- weblogic, websphere, jboss etc.