Java> = 8在带有instanceof instance的静态上下文中在接口上调用默认方法？

Question

我正在打字，我想知道如何在静态上下文中调用默认方法，我有一个这样的代码段。

interface InterfaceWithDefaultMethod{  
   public default void saySomething(final int a,final int b){System.out.println(String.format("Parameters are %d %d",a,b));}
}
public class StaticsMethodIsNotOverriden2 implements InterfaceWithDefaultMethod {
   public static void main(String[] args) {
      final StaticsMethodIsNotOverriden2 clazz = new StaticsMethodIsNotOverriden2();
      clazz.saySomething(13,20);//Overriden method call with 13 20
      clazz.callDefaultSaySomethingFromInstance();//Parameters are 1 2        
      /*HOW CALL public default void saySomething(final int a,final int b) METHOD HERE....????*/
      clazz.InterfaceWithDefaultMethod.super.saySomething(1, 2);/*no enclosing instance of type InterfaceWithDefaultMethod is in scope*/        
   }    

   @Override
   public void saySomething(int a, int b) {
      System.out.println(String.format("Overriden method call with %d %d",a,b));
   }
   //THIS IS WHAT A WANT TO DO BUT IN STATIC CONTEXT...
   private void callDefaultSaySomethingFromInstance(){
      InterfaceWithDefaultMethod.super.saySomething(1, 2); /*CALLING DEFAULT METHOD FROM INSTANCE CONTEXT*/       
   }
}

可以使用StaticsMethodIsNotOverriden2实例从静态上下文调用InterfaceWithDefaultMethod-> saySomething方法的默认方法吗？

很抱歉，问题很简单。

这是行不通的。

Answer 1

否。default方法是实例方法，在这种情况下，将启动动态绑定。没有任何方法可以让重写方法的客户端强制调用超级实现。这只能在子类中完成（就像您在中所做的那样callDefaultSaySomethingFromInstance）

您唯一的选择是在子类中公开一个不同的方法，并使该方法调用已实现的接口的默认方法：

class StaticsMethodIsNotOverriden2 implements InterfaceWithDefaultMethod {
    public static void main(String[] args) {
        ...
        clazz.superSaySomething(1, 2);
    }

    //a different name/signature needed
    public void superSaySomething(int a, int b) {
        System.out.println(String.format("Forcing super method call with %d %d", a, b));
        //the subclass calls default method
        InterfaceWithDefaultMethod.super.saySomething(a, b); 

    }

    @Override
    public void saySomething(int a, int b) {
        System.out.println(String.format("Overriden method call with %d %d", a, b));
    }

    ...
}