What are the keywords used to define interfaces in Java?

The keyword for defining interfaces in Java is "interface". "Interface" is the keyword for interface operations in object-oriented programming languages. Its function is to combine required members to encapsulate a set of certain functions. An interface cannot be instantiated directly, nor can it contain any code for members, only the members themselves are defined.

The keyword to define an interface in Java is interface

interface keyword

Interface is a keyword for interface operations in object-oriented programming languages. Its function is to combine the required members to encapsulate a set of certain functions. It is like a template in which the members that an object must implement are defined, through a class or structure. The interface cannot be instantiated directly, that is, ICount ic=new iCount() is wrong. The interface cannot contain any code for the members, only the members themselves are defined. The specific code for interface members is provided by the class that implements the interface. Interfaces are declared using the interface keyword.

Interface is a concept parallel to class
Java interface is a series of method declarations and a collection of method characteristics. An interface only has method characteristics but no method implementation. Therefore, these methods can be implemented by different classes in different places, and these implementations can have different behaviors (functions)

① The interface can be regarded as a special abstract class, which is a combination of constants and abstract methods Collections cannot contain variables. General methods

interface AA{
    //常量 : 所有的常量都用public static finial修饰 默认的,写不写都有
    int I = 15;//  public static final int I = 12;//  public static final boolean FLAG = false;
    
    /*抽象方法 
     * 
     * 抽象方法:所有的都用public abstract 修饰
            写不写都有
     * */
    void method1();
    void method2();//  public abstract void method1();//  public abstract void method2();
    }

② The interface has no constructor

③The interface defines a function, which can be implemented by classes (implements)

class CC  implements AA{
    public void method1() {
        
    }
    public void method2() {
        
    }
    }

④ A class that implements an interface must rewrite all abstract methods before it can be instantiated. If all abstract methods are not rewritten, this class is still an abstract class

abstract class BB implements AA{
    }

⑤ Inheritance in java is single inheritance, but a class can implement multiple interfaces.
Interface TZ

interface TZ{
    void method3();}

Class CC implements multiple interfaces

class CC  implements AA,TZ{
   public void method1() {
       
   }
   public void method2() {
       
   }
   public void method3() {
           
   }
   }

⑥ Between interfaces and interfaces There is also an inheritance relationship between them, and multiple inheritance can be achieved.
Interface MM inherits interface TZ, AA

//java 中接口之间仍为继承关系!(多继承)interface MM extends TZ,AA{
   void method4();
   }

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