Interface learning

interface

• General class : Only concrete implementation
• abstract class : Specific implementation and specification ( Abstract method ) There are !
• Interface : Only norms ! I can't write by myself , Professional constraints
• Interface is specification , It defines a set of rules , In the real world “ If you are … Must be able to …” Thought . If you are an angel , Must be able to fly . If you are a car , You have to be able to run . If you're a good person , You have to get rid of the bad guys ; If you are a bad person , You have to bully good people .
• The essence of an interface is a contract , Just like the law of our world . When it's done, everyone follows .
  OO The essence of , It's the abstraction of objects , The best way to do this is through interfaces . Why do we talk about design Patterns are only for languages with abstract capabilities ( such as c++、java、c# etc. ), It's because of the design pattern , In fact, it's how to abstract reasonably .
• The keyword of the declaration class is class, The key to declare the interface is interface

 package com.oop.Demo08;

//interface  Defined keywords  , Interfaces need to have implementation classes 
public interface UserService {
    

    // Definition  public static final
    public static final int age = 99;

    // All definitions in an interface are actually abstract  public abstract
    public abstract void add(String name);

    void delete(String name);

    void update(String name);

    void query(String name);
    // Interface function 
    /* 1. constraint  2. Define some methods   Let different people realize  3. public abstract 4.public static final 5. Interface cannot be instantiated   There is no constructor in the interface  6.implements Multiple interfaces can be implemented  7. You have to override the methods in the interface  * */
}
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    package com.oop.Demo08;

public interface TimeService {
    
    void run();
}
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    package com.oop.Demo08;
// abstract class ：extents
// class   Interface can be implemented  implement  Interface 
// The class that implements the interface   You need to rewrite the methods in the interface 

// Multiple inheritance   Using interfaces to implement multiple inheritance 
public class UserServiceImpl implements UserService,TimeService{
    
    @Override
    public void add(String name) {
    

    }

    @Override
    public void delete(String name) {
    

    }

    @Override
    public void update(String name) {
    

    }

    @Override
    public void query(String name) {
    

    }

    @Override
    public void run() {
    

    }
}