① format:
1 "static modifications, called static members, non-static modifications, called non-static members.
② memory location:
1 "static modification, in the static area method area, the non-static modification of an object in the heap.
③ life cycle:
1 "static modified, with the load and load class, with the demise of class die out with the creation of non-static objects and loaded, with the demise of objects and die.
④ invocation:
1 "static modified, invoked by class name. Members, non-static modification, Members called through the object.