Assuming you have installed Java in c:\Program Files\java\jdk directory −
Right-click on 'My Computer' and select 'Properties'.
Click the 'Environment variables' button under the 'Advanced' tab.
Now, alter the 'Path' variable so that it also contains the path to the Java executable. Example, if the path is currently set to 'C:\WINDOWS\SYSTEM32', then change your path to read 'C:\WINDOWS\SYSTEM32;c:\Program Files\java\jdk\bin'.
Assuming you have stored your Java programs in c:\myprograms\ directory −
Right-click on 'My Computer' and select 'Properties'.
Click the 'Environment variables' button under the 'Advanced' tab.
Now, add the 'CLASSPATH' variable and set the path to the c:\myprograms\'.