public interface Callback {
    void completed();
}

public class AsynchronousTask extends Thread {
    
    private Callback callback;
    private int result;
    
    public AsynchronousTask(final Callback callback){
        this.callback = callback;
    }
    
    @Override
    public void run() {
        try {
            //Do some "work"
            sleep(5);
            
            result = 42;
        } 
        catch (InterruptedException ex) { }
        
        callback.completed();
    }

    public int getResult() {
        return result;
    }
}