"Java Summary" final keyword, abstract class, interface, inner class

Final

1. The final decorated class, which indicates that the class cannot be inherited
2. The final modification method, which indicates that this method cannot be overridden
3. Final modifier constant (constant capitalization), indicating that constants cannot be modified
4. Static final-modified constants, representing global constants

Abstract class

• Class that uses the abstract modifier, which is a class of abstraction
• Using the abstract modified method, as an abstraction, this method only life is not implemented
• Classes that contain abstract methods must be abstract classes
• Abstract class cannot be instantiated, subclass of abstract class must override abstract method of parent class
• Cannot use the abstract modifier property, private method, constructor, static method, final method

/*我为抽象类*/abstract calss A {    abstractvoid m();}

Interface (interface)

• An interface is a special abstract class with no attributes, only methods
• The interface is implemented by the class, and the implementing class must override all the methods in the interface
• Interface is a way to implement multiple inheritance in Java
• Interfaces are public-decorated, and methods are public

/*声明一个接口*/publicinterface Runner {    publicvoidrun();}/*实现接口*/publicclass implements Runner {    publicvoidrun() {        System.out.printf("我会跑！");    }}

Inner class

In Java, one class is allowed to define another class, which becomes an outer class, which is called an inner class

• Inner classes can be declared as final
• Inner classes can be decorated as private or protected
• The inner class can be static, and the non-static member variable of the outer class cannot be used at this time

 Public classTest { Public Static void Main(string[] args) {A A =NewA (); A.B B = A.NewB (); B.M (3); }}class A {Private ints =1; Public classBPrivate ints =2; Public void m(ints) {System. out. println (s);//3 Local VariablesSystem. out. println ( This. s);//2 objects for inner classesSystem. out. println (A. This. s);//1 objects of the outer class}    }}

Anonymous inner class

General Swing is used more
Here is a use of the inner class

button.addListener(    new OnClickListener() {        //实现方法     });

"Java Summary" final keyword, abstract class, interface, inner class