What is the difference between a Java API and a library?

Question

I know that an API is called a set of functions used to call something, and a library is a collection of classes, but what is actually API in package like java.lang

Answer 1

Straight from Wikipedia:

In computer science, an application programming interface (API) is an interface that defines the ways by which an application program may request services from libraries

Java contains many libraries in those packages (Swing, etc.), and the API is the interface by which we request services (perform actions, etc.).