Java callback example

interface Callable
{
    public void callBackMethod();
}

class Worker
{
    // Worker gets a handle to the boss object via the Callable interface.
    // There's no way this worker class can call any other method other than
    // the one in Callable.
    public void doSomeWork(Callable myBoss)
    {
        myBoss.callBackMethod();
        // ERROR!
        //myBoss.directMethod();
    }
}

class Boss implements Callable
{
    public Boss()
    {
        // Boss creates a worker object, and tells it to do some work.
        Worker w1 = new Worker();
        // Notice, we're passing a reference of the boss to the worker.
        w1.doSomeWork(this);
    }
    public void callBackMethod()
    {
        System.out.println("What do you want?");
    }
    public void directMethod()
    {
        System.out.println("I'm out for coffee.");
    }
}

public class CallBack
{
    // Main driver.
    public static void main(String[] args)
    {
        Boss b = new Boss();
        b.directMethod();
    }
}