匿名内部类

interface Message{
    public void print(); 
}

public class Demo{
    public static void main(String arg[]){
        fun(new Message() {
            public void print (){
                System.out.println("Hello world") ;    
            }
        }) ;
        
    }    
    
    public static void fun(Message msg){
        msg.print();
    }
}