What is the difference amongst JVM Spec, JVM Implementation, JVM Runtime

Question

Hi I read the following words but I like to know differences among them... JVM Spec, JVM Implementation, JVM Runtime

Answer 1

JVM Spec: document describing how the JVM should behave.

JVM Implementation: an implementation of a JVM based on the JVM Spec.

JVM Runtime: an instance of a JVM implementation.

Answer 2

the jvm spec is just a document that describes how a java virtual machine must work. Anybody is free to take that spec and build their own jvm implementation. Think of the spec like a blueprint, and the implementation like the house you build from it. As a contractor you are free to make minor changes, different materials etc, as long as the blueprint is followed.

The JVM runtime is the implementation. The runtime is what is execute when you use the java command. As i said, different companies have made their own implementations of the jvm runtime from the spec.