java what is a callback code example

Example: java callbacks

interface CallBack {                   //declare an interface with the callback methods, so you can use on more than one class and just refer to the interface
    void methodToCallBack();
}

class CallBackImpl implements CallBack {          //class that implements the method to callback defined in the interface
    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();       //because of the interface, the type is Callback even thought the new instance is the CallBackImpl class. This alows to pass different types of classes that have the implementation of CallBack interface
        caller.register(callBack);
    }
}