Alternate of C# Events in Java

Question

I am .Net developer. i want to know that is there any event handling mechanism in Java for Events Handling like C#.

what i want to do is i want to raise/fire an event form my class upon some condition. and consumer of this class should register that event and write event handling method.

this can be done easily in C#. i have to implement this thing in Java.

after googling out i found some links but all those are talking about GUI events in AWT and swing.

can any one help me out.

Answer 1

Although most of the examples will be to do with GUI events, the principles are basically the same. You basically want an interface or abstract class to represent a handler for the event, e.g.

public interface EventHandler
{
    // Change signature as appropriate of course
    void handleEvent(Object sender, EventArgs e);
}

then the publisher of the event would have:

public void addEventHandler(EventHandler handler)
public void removeEventHandler(EventHandler handler)

It would either keep a list of event handlers itself, or possibly have them encapsulated in a reusable type. Then when the event occurs, you just call handleEvent in each handler in turn.

You can think of delegate types in C# as being very similar to single-method interfaces in Java, and events are really just an add/remove pair of methods.

Answer 2

I love C# Events,

They are simple to use and convenient. i missed them in java so wrote a small utility class that mimics the very basics of C# Event.

• using java 8 (for lambdas)
• no += operator, instead call .addListener((x) -> ...)
• to trigger an event, call .broadcast(<EventArgs insance>)

Online Demo - https://repl.it/DvEo/2

---

Event.java

import java.util.HashSet;
import java.util.Set;
import java.util.function.Consumer;

public class Event {
    private Set<Consumer<EventArgs>> listeners = new HashSet();

    public void addListener(Consumer<EventArgs> listener) {
        listeners.add(listener);
    }

    public void broadcast(EventArgs args) {
        listeners.forEach(x -> x.accept(args));
    }
}

• You may want com.google.common.collect.Sets.newConcurrentHashSet() for thread safety

EventArgs.java

public class EventArgs {
}