Callback in Java vs Scripting Languages

Question

I was looking at How do I perform a JAVA callback between classes?. And the first answer, answered my query.

interface CallBack {
    void methodToCallBack();
}

class CallBackImpl implements CallBack {
    public void methodToCallBack() {
        System.out.println("I've been called back");
    }
}

class Caller {

    public void register(CallBack callback) {
        callback.methodToCallBack();
    }

    public static void main(String[] args) {
        Caller caller = new Caller();
        CallBack callBack = new CallBackImpl();
        caller.register(callBack);
    }
}

However, it challenges my concept of callback from scripting languages like JavaScript. Where implementation of callback functions are passed from the caller. for example,

function IWillCallTheCallBack(callback) {
      callback();
}

Can anyone explain the difference between callback in Java vs other programming language.

Callbacks aren't really used in Java. In Java we achieve polymorphism through inheritance and interfaces instead. We can pass around instances of classes instead of functions. — byxor, Jan 15 '17 at 13:23

score 0 · Answer 1 · answered Feb 24 '20 at 17:05

One possible way might be to use a lambda of a Runnable. The advantage of this is that it can be called back asynchronously, on another Thread, if you want.

public class CallbackTest {

    public static void run(Runnable callback) {
        callback.run();
    }

    public static void main(String[] args) {
        run(()-> System.out.println("I've been called"));
    }
}

Callback in Java vs Scripting Languages

1 Answers1