Class modifiers, member variable modifiers, method modifiers in Java

Class modifier:
Public (access control), which declares a class as a common class, can be accessed by any object, and the main class of a program must be a public class.

Abstract, declaring a class as an abstract class, without implementing a method, requires a subclass to provide a method implementation.

Final, a class life is final (that is, a non-inheriting class), indicating that he cannot be inherited by another class.

Friendly, the default modifier, only objects in the same package can use such a class.

Access permissions for member variables and methods

Class modifiers, member variable modifiers, method modifiers in Java