Java is compiled to an intermediate form called byte-code. 
A Java program never really executes natively on the host 
machine. Rather a special native program called the Java 
interpreter reads the byte code and executes the 
corresponding native machine instructions. Thus to port 
Java programs to a new platform all that is needed is to 
port the interpreter and some of the library routines. Even 
the compiler is written in Java. The byte codes are 
precisely defined, and remain the same on all platforms.