EventEmitter

About

This project is a Java event emitter based on Java 8's FunctionalInterface. The emitter maps Event classes to Consumers. If you haven't been introduced to these Java 8 features, you should probably read up on them. I'm not going to explain them here.

The event emitter is really simple. In fact, it's more documentation than it is code. It basically stores Consumers in a HashMap keyed by their respective Event class. When registering a listener, it is required that the Consumer is able to accept an instance of the Event it is being registered to.

Sadly, I couldn't quite abuse Java generics to make this system perfect, so there is some casting going on. It's all safe though, since an Event will never be registered to a Consumer that is unable to accept it.

Usage

Super easy.

First, instantiate an EventEmitter

import me.hgal.event.EventEmitter;

EventEmitter emitter = new EventEmitter();

Next, register a listener to an event. A listener is any method that accepts only one parameter: an instance of the event. Lambdas will do the trick.

import SimpleEvent; //events implement me.hgal.event.Event
// Pretend SimpleEvent accepts one argument, and toString() returns it

emitter.on(SimpleEvent.class, e -> System.out.println(e.toString()));

Or if you prefer not to use lambdas...

class MyListener {

    public MyListener(EventEmitter emitter) {
        emitter.on(SimpleEvent.class, this::myMethod);
    }

    void myMethod(SimpleEvent e) {
        System.out.println(e.toString());
    }

}

Now you can fire an event

emitter.emit(new SimpleEvent(1));
// > 1

You can even store an event and apply side effects

emitter.on(SimpleEvent.class, e -> { e.setVal(0) });

Event e = emitter.emit(new SimpleEvent(1));
System.out.println(e.toString())
// > 0