Why Java Is Called Platform Independent Although It Needs J2ee Plateform.?

Platform independent means,the java compiled program can be
run on any operating system.because when you compile a
program you will get a class file which contains byte code
which is specific to java. That byte code can understand by
jvms (java virtual machines).for different operating
systems different jvms will be there.so the jvm will
convert the byte code into machine understandable code.so
as the jvm is different for different operating systems no
need to worry much,that will take care of explaining to the
os.ok.