Detailed description of methods in the interface

One . Interface profile

       Interface (interface), yes java A reference data type in , It can be seen as a collection of methods , Its interior mainly encapsulates the methods , Contains abstract methods (JDK 7 And before ), Default and static methods (JDK 8), Private method (JDK 9).

Two . Use examples .

1. Define format :
public interface The name of the interface {
       // Abstract method
       // The default method
       // Static methods
       // Private method
}
2. Class definition of implementation interface :
public class Class name implements The interface name {
       // Implement abstract methods in the interface ( must )
       // Override the default method in the interface ( Optional )
}
3. Be careful :

1. Interface cannot create object , But it can be realized , Subclasses of an interface must implement all abstract methods in the interface . The default method is optional .
2. Variable cannot be defined in interface , You can define constants , By default public static final modification ( Forever immutable
3. There is no constructor in the interface , No code blocks

3、 ... and . Various methods are explained in detail .

1. Abstract method :
   Use abstract modification , For subclass implementation
   public abstract void method();

Be careful : All methods are in the interface ( By definition ) It's all abstract methods , therefore abstract Keywords can be left blank , Interfaces represent a collection of external behaviors , In the declaration of the method , All defaults to public, therefore public Or not It can be written directly as (void methods);

2. The default method
   Use default modification , Do not omit , For subclasses to call or override ( Can only be called through the final implementation class , Cannot call... Through an abstract class )
   public default void method(){
          // Execute statement
   }

3. Static methods
   use static modification , For the interface to call directly . Can only be called by interface name . Subclasses cannot inherit or override
   public static void method(){
          // Execute statement
   }

4. Private method
   Use private modification , For the default method or static method in the interface
   private void method(){
          // Execute statement
   }

Examples of using default methods :
example :( Only through the final implementation class ( No, abstract modification ) call , Cannot call... Through an abstract class )

        public interface Test{
    
             public default void print(){
    
                  System.out.print(" I'm the default method ");
             }
         }
         public class TestImpl implements Test{
    
             //1. Write nothing , You can call... Through an object 
             //2. Or rewrite  
         }

Use of static methods :
example :( Can only be called by interface name )

  public interface Test{
    
         public static void print(){
    
             System.out.ptinr(" I'm a static method ");
         }
     }
     public class TestImpl  implements Test{
    
         // Cannot override or inherit static methods 
     }