what is jvm
JVM is an acronym for Java Virtual Machine;
it is an abstract machine which provides the runtime environment
in which Java bytecode can be executed.
It is a specification which specifies the working of Java Virtual Machine.
Its implementation has been provided by Oracle and other companies.
Its implementation is known as JRE.
JVMs are available for many hardware and software platforms
(so JVM is platform dependent). It is a runtime instance which is
created when we run the Java class.
There are three notions of the JVM: specification, implementation, and instance.
