C#.net events and java

Question

so i'm coming from a c#.net background,, and i'm trying to do this in java

Class A{

public delegate void EventHandler();

    public static event EventHandler workComplete();

void doWork(){

    // DO WORK  

}

void onWorkComplete(){

    // Riase Event

    workComplete();

}

} Class Main{

A a = new A();

a.workComplete += () -> {

    // On Class A Complete Work

    Console.WriteLine("Work Complete");

`
}; }

I search for delegates in Java sense event are requers delegates as in c#.net,, but it's look like that Java don't have delegates ,, then i star to search how events work in Java then i fall into three things 1- Action Listener 2- Events Listener 3- and a lot of interfaces 4- observer pattern

and it's all mix up to me ,, maybe because i just understand C# events that's uses delegates.

So if any one could give a sample example like the c#.net code above ,,, in Java that's will be a very helpful.

Thank You.

Java uses the observer pattern (commonly reffered to as Listeners in java) for events. Google java listeners for examples. — Philip Pittle
– Philip Pittle, Commented Nov 30, 2014 at 18:08

Eduard Dumitru · Accepted Answer · 2014-11-30 15:15:54Z

I'm going to make this quick and dirty. Unfortunately, in Java you'll have to write more code to produce the same results.

I've split the code into 3 sections:

an interface which kind of resembles the delegate declaration
class A which contains the event declaration, subscription logic and raise logic
class B which is the "event consumer" and which declares the event handler

Good luck!

// this is what you used to have as a delegate declaration {
public interface IWorkCompletedListener {
    public void someMethodName(Object sender, Object args);
}
// }

// class A will be the event provider
public class A {

    // this is what you used to have for an event declaration {
    // used for the storage of listeners
    private static Vector<IWorkCompletedListener> workComplete = new Vector<IWorkCompletedListener>();

    // used for +=
    public static void addWorkCompleteListener(IWorkCompleteListener listener) {
        A.workComplete.add(listener);
    }
    // used for -=
    public static void removeWorkCompleteListener(IWorkCompleteListener listener) {
        A.workComplete.remove(listener);
    }
    // }

    // this is what you would use to raise the event {
    private static void raiseWorkCompletedListener(Object sender, Object args) {
        for (IWorkCompletedListener listener : A.workComplete)
            listener.someMethodName(sender, args);
    }
    // }

    // and the test code
    public static void doWork() {
        // Stuff goes here
        A.raiseWorkCompletedListener(null, null);
    }

}

// class B will be the event consumer
public class B {

    public static void subscribeAndCallDoWork() {
        // this is what += used to be
        A.addWorkCompleteListener(new IWorkCompletedListener {
            public void someMethodName(Object sender, Object args) {

                // I didn't want to force class B to implement the interface
                // hence I used an anonymous interface implementation
                // from which I'm calling the "event handler"
                B.onWorkCompleted(sender, args);

            }
        });

        A.doWork();
    }

    private static onWorkCompleted(Object sender, Object args) {
       // expect to be called here
    }

}

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