Virtual Machine - ( JVM )
execute a Java program, you run a program called
a bytecode interpreter, which in turn reads
the bytecodes and executes your Java program.
The Java bytecode interpreter is often also
called the Java virtual machine or the Java
bytecodes are a special set of machine instructions
that are not specific to any one processor or
computer system. A platform-specific bytecode
interpreter executes the Java bytecodes. The
bytecode interpreter is also called the Java
virtual machine or the Java runtime interpreter.
Java virtual machine, which is a component of
the runtime system, is responsible for interpreting
the bytecodes and making the appropriate system
level calls to the native platform. It is at
this point where platform independence is achieved
by Java; the bytecodes are in a generic form
that is only converted to a native form when
processed by the virtual machine.
The JVM concept allows a layer of translation
between the executable program and the machine-specific
code. In a non-Java compiler, the source code
is compiled into machine- specific assembly
code. In doing this, the executable limits itself
to the confines of that machine architecture.
Compiling Java code creates an executable using
JVM assembly directives. The difference of the
two approaches is quite fundamental to the portability
of the executable. Non-Java executables communicate
directly with the platform's instruction set.
Java executables communicate with the JVM instruction
set, which is then translated into platform-specific
A Java Virtual Machine starts execution by invoking
the method main of some specified class, passing
it a single argument, which is an array of strings.