Java includes predefined class packages (aka Java class libraries) as part of the Java installation.
  • A class library is a collection of classes (e.g. System.Scanner.String)
  • Packages: Java Standard Classes are organized into packages

Some specific package/libraries are listed below.

  •  Packages applets java.applet,
  • Language extensions  java.lang,
  •  utilities java.util,
  • formatters java.text,
  • Input Output: io,
  • GUI java.awt and javax.swing,
  • network services,
  • precision math java.math,
  • database management java.sql,
  • security
Mostly use "java.lang"