To compile Java programs after you have installed the SDK, open a console. In Windows, go to Start > Run and type cmd to get a command prompt.
Note that if you have multiple JDKs on your system, you may need to supply the –source 1.5 flag to the javac command to ensure that your code is compiled correctly.
C:\garage\src>javac -source 1.5 net\javagarage\demo\MyProgram.java
This compiles the Java source code into a class file in the same directory.
If all goes well during compilation, you get a new command prompt, and nothing else. You are now ready to run your program using the java command.