internal versus external libraries Java

Question

What is the difference between internal and external libraries in Java?

For example,

   import java.util.*;
   import java.io.File;

Is java.util and/or java.io an internal library, external library, or something else? Thanks!

Answer 1

Conceptually, an internal library is either "a library that is provided as (effectively) "part of the language itself," or "a library that is known only to your (big) project." In one case, only the language-vendor has control of it. In the other, only you do.

An external library is something that comes from an outside source. (Hence, neither you nor the language-vendor "owns" it.) Your project references it, and depends on (a certain version of) it such that "it cannot live without it," but it is not "(just) a part of this project."