SETTING JAVA

In order to develop Java applications you need the Java Software Developer Kit (JDK) installed. The JDK includes tools useful for developing and testing programs written in the Java programming language and running on the Java platform.Java is freely available on Oracle's Website. Download the latest version of JDK (Java Development Kit) on your machine. The most current version at the time of writing is the Java 8 SDK.

Install Java

Latest version of Java can be downloaded from Java Website

http://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html

Once java is downloaded, it can be installed like any other software (.exe) in your Windows system.Once you have installed Java on your machine you would need to set environment variable to point to correct installation directory.

An Environment variable is an object on a computer that stores a value(key-value pair), which can be referenced by one or more software programs in Windows.

PATH and CLASSPATH

If you are saving the java source file inside the jdk/bin directory, path is not required to be set because all the tools will be available in the current directory. But If you are having your java file outside the jdk/bin folder, it is necessary to set path of JDK. After installing the software, the JDK directory will have the structure shown below.

Update the PATH Environment Variable (Microsoft Windows)

You can run Java applications just fine without setting the PATH environment variable. Or, you can optionally set it as a convenience.

Set the PATH environment variable if you want to be able to conveniently run the executables (javac.exe, java.exe, javadoc.exe, and so on) from any directory without having to type the full path of the command. If you do not set the PATH variable, you need to specify the full path to the executable every time you run it, such as:

C:\Java\jdk1.7.0\bin\javac MyClass.java

The PATH environment variable is a series of directories separated by semicolons (;). Microsoft Windows looks for programs in the PATH directories in order, from left to right. You should have only one bin directory for the JDK in the path.

It is useful to set the PATH environment variable permanently so it will persist after rebooting. To make a permanent change to the PATH variable, use the System icon in the Control Panel. The precise procedure varies depending on the version of Windows:

Windows XP

1. Select Start, select Control Panel. double click System, and select the Advanced tab.
2. Click Environment Variables. In the section System Variables, find the PATH environment variable and select it. Click Edit. If the PATH environment variable does not exist, click New.
3. In the Edit System Variable (or New System Variable) window, specify the value of the PATH environment variable. Click OK. Close all remaining windows by clicking OK.

Windows Vista:

1. From the desktop, right click the My Computer icon.
2. Choose Properties from the context menu.
3. Click the Advanced tab (Advanced system settings link in Vista).
4. Click Environment Variables. In the section System Variables, find the PATH environment variable and select it. Click Edit. If the PATH environment variable does not exist, click New.
5. In the Edit System Variable (or New System Variable) window, specify the value of the PATH environment variable. Click OK. Close all remaining windows by clicking OK.

Windows 7:

1. From the desktop, right click the Computer icon.
2. Choose Properties from the context menu.
3. Click the Advanced system settings link.
4. Click Environment Variables. In the section System Variables, find the PATH environment variable and select it. Click Edit. If the PATH environment variable does not exist, click New.
5. In the Edit System Variable (or New System Variable) window, specify the value of the PATH environment variable. Click OK. Close all remaining windows by clicking OK.

Update the PATH Variable (Solaris and Linux)

You can run the JDK just fine without setting the PATH variable, or you can optionally set it as a convenience. However, you should set the path variable if you want to be able to run the executables (javac, java, javadoc, and so on) from any directory without having to type the full path of the command. If you do not set the PATH variable, you need to specify the full path to the executable every time you run it, such as:
% /usr/local/jdk1.7.0/bin/javac MyClass.java

To find out if the path is properly set, execute:
% java -version

This will print the version of the java tool, if it can find it. If the version is old or you get the error java: Command not found, then the path is not properly set.

To set the path permanently, set the path in your startup file.

For C shell (csh), edit the startup file (~/.cshrc):
set path=(/usr/local/jdk1.7.0/bin $path)

For bash, edit the startup file (~/.bashrc):
PATH=/usr/local/jdk1.7.0/bin:$PATH
export PATH

For ksh, the startup file is named by the environment variable, ENV. To set the path:
PATH=/usr/local/jdk1.7.0/bin:$PATH
export PATH

For sh, edit the profile file (~/.profile):
PATH=/usr/local/jdk1.7.0/bin:$PATH
export PATH

Then load the startup file and verify that the path is set by repeating the java command:

For C shell (csh):
% source ~/.cshrc
% java -version

For ksh, bash, or sh:
% . /.profile
% java -version

Checking the CLASSPATH variable (All platforms)

The CLASSPATH variable is one way to tell applications, including the JDK tools, where to look for user classes. (Classes that are part of the JRE, JDK platform, and extensions should be defined through other means, such as the bootstrap class path or the extensions directory.)

The preferred way to specify the class path is by using the -cp command line switch. This allows the CLASSPATH to be set individually for each application without affecting other applications.Setting the CLASSPATH can be tricky and should be performed with care.

The default value of the class path is ".", meaning that only the current directory is searched. Specifying either the CLASSPATH variable or the -cp command line switch overrides this value.

To check whether CLASSPATH is set on Microsoft Windows NT/2000/XP, execute the following:
C:> echo %CLASSPATH%

On Solaris or Linux, execute the following:
% echo $CLASSPATH

If CLASSPATH is not set you will get a CLASSPATH: Undefined variable error (Solaris or Linux) or simply %CLASSPATH% (Microsoft Windows NT/2000/XP).

To modify the CLASSPATH, use the same procedure you used for the PATH variable.

Difference between PATH and CLASSPATH in Java

• PATH is an environment variable which is used to locate JDK binaries like "java" or "javac" command used to run java program and compile java source file. Where as CLASSPATH environment variable is used by System or Application ClassLoader to locate and load compile Java bytecodes stored in .class file.
• PATH can not be overridden by any Java settings but CLASSPATH can be overridden by providing command line option -classpath or -cp to both "java" and "javac" commands or by using Class-Path attribute in Manifest file inside JAR archive.
• PATH environment variable is used by OS to find any binary or command typed in shell, applicable for both Windows and Linux environment while CLASSPATH is only used by Java ClassLoaders to load class files.
• You include JDK_HOME/bin directory in PATH environment variable while, to set CLASSPATH in Java you include all those directory where you have put .class file or JAR file which is required by your Java application.

How to Check if Java is Installed

To check if your java is installed properly open Command Prompt . To open command prompt write “CMD” in run command and hit enter. In the command prompt window write “java -version“. If your java is installed properly and all environment variables are configured correctly it will show the version of Java installed . Information reflected on the command prompt will be like

If there is any problem while installing or in setting up the environment variable, output on command prompt will be like
'java' is not recognized as an internal or external command,operable program or batch file.