匿名内部类-getClass（）

Question

I have written the following code:

public class AnonymousClasses {

    public void sayHello(){

    }


public interface GreetingModule {
    public void sayHello();
}

public static void main(String[] args) {
    AnonymousClasses jonny = new AnonymousClasses(){
        @Override
        public void sayHello() {
            System.out.println("Hey");
        }
    };
    AnonymousClasses john = new AnonymousClasses(){
        @Override
        public void sayHello() {
            System.out.println("Hi");
        }
    };


    GreetingModule greeting = new GreetingModule() {

        @Override
        public void sayHello() {
            System.out.println("Hello");
        }


    };

    jonny.sayHello();
    john.sayHello();
    greeting.sayHello();

    System.out.println(jonny.getClass());
    System.out.println(john.getClass());
    System.out.println(greeting.getClass());

}

The output is of course:

Hey

Hi

Hello

class AnonymousClasses$1

class AnonymousClasses$2

class AnonymousClasses$3

However, when I edit my code as follows:

public class AnonymousClasses {

    private final GreetingModule greetingModule;

    public AnonymousClasses(GreetingModule greetingModule) {

        this.greetingModule = greetingModule;
    }

    public void saySomething() {
        greetingModule.sayHello();
    }


public interface GreetingModule {
    public void sayHello();
}

public static void main(String[] args) {
    AnonymousClasses jonny = new AnonymousClasses(new GreetingModule(){
        @Override
        public void sayHello() {
            System.out.println("Hey");
        }
    });
    AnonymousClasses john = new AnonymousClasses(new GreetingModule(){
        @Override
        public void sayHello() {
            System.out.println("Hi");
        }
    });


    GreetingModule greeting = new GreetingModule() {

        @Override
        public void sayHello() {
            System.out.println("Hello");
        }


    };

    jonny.saySomething();
    john.saySomething();
    greeting.sayHello();

    System.out.println(jonny.getClass());
    System.out.println(john.getClass());
    System.out.println(greeting.getClass());

}

the output is:

Hey

Hi

Hello

class AnonymousClasses

class AnonymousClasses

class AnonymousClasses$3

Can somebody explain me, why there is no name of the inner class with a dolar in the first two getClass() methods? Is it still an inner class?

Answer 1

You are creating instances of the class on the second sample:

AnonymousClasses jonny = new AnonymousClasses(new GreetingModule(){
    @Override
    public void sayHello() {
        System.out.println("Hey");
    }
});

To create a anonymous subclass of it would like:

AnonymousClasses jonny = new AnonymousClasses(new GreetingModule(){
    @Override
    public void sayHello() {
        System.out.println("Hey");
    }
}) {
      // Overriding anything here is optional
};

Answer 2

$ symbol comes with the class name when there is a new unnamed implementation of the class.

In the first example , you are creating new implementations of AnonymousClasses in each case.

AnonymousClasses jonny = new AnonymousClasses(){
        @Override
        public void sayHello() {
            System.out.println("Hey");
        }
};

It's similar to creating an object of a subclass with AnonymousClasses as the parent class. In this case, since there is no name for the subclass, JVM appends $1 to its parent's name to create a unique name.

In the second example , you are just creating new objects of same implementation of AnonymousClasses. It might seem similar, but if you notice carefully, each time you are creating a new implementation of GreetingModule interface which is passed to the constructor of AnonymousClasses.

In both the cases, there is no inner class. In first example, they are just the objects of subclasses of AnonymousClasses and in second case, they are objects of the same AnonymousClasses.