抽象类和匿名类 [英] abstract class and anonymous class

问题描述

abstract class Two {
    Two() {
        System.out.println("Two()");
    }
    Two(String s) {
        System.out.println("Two(String");
    }
    abstract int  display();
}
class One {
    public Two two(String s) {
        return new Two() {          
            public int display() {
                System.out.println("display()");
                return 1;
            }
        };
    }
}
class Ajay {
    public static void main(String ...strings ){
        One one=new One();
        Two two=one.two("ajay");
        System.out.println(two.display());
    }
}

我们不能实例化一个抽象类那么为什么函数Two two(String s)能够创建一个抽象类Two的实例???????

we cannot instantiate an abstract class then why is the function Two two(String s) able to create an instance of abstract class Two ????

推荐答案

它不会创建抽象 Two 的实例.它创建了一个具体的匿名类，该类扩展了 Two 并对其进行了实例化.

It does not create an instance of abstract Two. It creates a concrete, anonymous class that extends Two and instantiates it.

这几乎等同于使用这样的命名内部类:

It's almost equivalent to using a named inner class like this:

class One {
    public Two two(String s) {
        return new MyTwo();
    }

    class MyTwo extends Two {
        public int display() {
            System.out.println("display()");
            return 1;
        }
    }
}

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