The most unique feature of java is platform independent. 
In any programming language soruce code is
compiled in to executable code . This cannot be run across all platforms. 
When javac compiles a java
program it generates an executable file called .class file.
class file contains byte codes. Byte codes are interpreted only by JVM’s . 
Since these JVM’s are made
available across all platforms by Sun Microsystems, we can execute this byte 
code in any platform. Byte
code generated in windows environment can also be executed in linux 
environment. This makes java platform independent