Guava學習筆記-簡化觀察者模式的實現

###問題描述
實現一個觀察者模式，監聽方法接受一個Integer參數，而且其打印出來

###本身實現

public static void main(String[] args) {
    EventSource eventSource = new EventSource();
    eventSource.register(new Listener());
    eventSource.print(1);
}

interface Print {
    void print(Integer integer);
}

static class EventSource implements Print {
    private Set<Print> listeners = Sets.newCopyOnWriteArraySet();

    public void print(Integer integer) {
        for (Print listener : listeners) {
            listener.print(integer);
        }
    }

    public void register(Print print) {
        listeners.add(print);
    }
}

static class Listener implements Print {
    public void print(Integer integer) {
        System.out.println(integer);
    }
}

###使用JDK實現

public static void main(String[] args) {
    EventSource eventSource = new EventSource();
    eventSource.addObserver(new Listener());
    eventSource.print(1);
}

static class EventSource extends Observable {
    public void print(Integer integer) {
        setChanged();
        notifyObservers(integer);
    }
}

static class Listener implements Observer {
    public void update(Observable o, Object arg) {
        System.out.println(arg);
    }
}

###使用Guava

public static void main(String[] args) {
    EventBus eventBus = new EventBus();
    eventBus.register(new Listener());
    eventBus.post(1);
}

static class Listener {
    @Subscribe
    public void print(Integer integer) {
        System.out.println(integer);
    }
}