Abstract class, interface, abstract class Interface

Abstract class, interface, abstract class Interface

Why use abstract classes:

If the subclass is not correctly rewritten, no prompt is displayed.

Assume that the code of the parent class is as follows:

public class USB {     public void QiDong(){                 }     public void TingZhi(){              }}

The code in the subclass is as follows: rewrite the method in the parent class

Public class UPan extends USB {public void Qidong () {// Qidong here is not a rewriting of the parent class function System. out. println ("U disk started");} public void TingZhi () {System. out. println ("the USB flash disk stops running ");}}

Such code will not report errors in Eclipse;

Abstract class: a class that does not know what it is.

Description: abstract class name

public abstract class USB {}

Abstract method: I don't know what the specific method is;

Writing Method: abstract return type function name (parameter); abstract method does not need to write function body

In a derived class, certain abstract methods are not implemented, but the derived class must be declared as an abstract class.
Abstract classes can have abstract methods or non-abstract methods. Abstract classes can also contain member variables.

public abstract class USB {      public  String JiaGe;     public abstract void QiDong();
     public abstract void TingZhi();         }

 

Interface:

The role of the interface: It mainly serves as a constraint. It can be understood that the code format of a large frame can only be written in the specified format.

Definition: file-New-interface // The first letter of the interface name plus an uppercase I

When defining an interface, the interface name should be an adjective or descriptive word.

Interface content as few as possible for convenient and flexible use-interface separation principle

Interface Name extends parent interface list {final type constant name = value; // specifies the format in which to write data. If the format is different from the format, public void method name (parameter) will be reported );}

Interface implementation:

Abstract class name extends parent class implements interface list {
}

 

As mentioned above, the interface serves as a constraint, so let's take a look at how it is constrained.

Create an interface-enter the following code in the interface

public interface IJiSuan {    public int a=0;        public void Suan(int a, int b);}

Then we create a new class-class add interface, click OK, the following code is automatically generated;

Public abstract class YunSuan implements IJiSuan {@ Override public void Suan (int a, int B) {// method stub automatically generated by TODO }}

If we change the method name to suan, an error is automatically reported.

 

Final can modify member variables (constants), member methods (not allowed to be rewritten), classes (not allowed to be inherited)