注册Java事件时，通常允许重复的侦听器？ [英] When registering for Java events, are duplicate listeners typically allowed?

问题描述

应该在调用add方法时检查重复的注册？如果是这样，当发现重复时应该怎么办？

Should an addListener method check for duplicate registrations when called? If so, what should happen when a duplicate is found?

final public class exampleCanFire {
    public void addFooListener(FooListener listener) {
      // Before adding listener to private list of listeners, should I check for duplicates?
    }
}

推荐答案

我的偏好是将它们存储在列表中，而不是检查重复项。这种方法的一些优点：

My preference is to store them in a List and not check for duplicates. Some advantages of this approach:

• 监听器以确定性顺序通知，可能将事件标记为消耗，导致不传播到


• 可以使用 CopyOnWriteArrayList 实现，它允许侦听器在通知回调期间自动删除而不使用 ConcurrentModificationException 被抛出（这是非常重要，并且是编写面向事件的代码时的经典支持）。

• Listeners are notified in a deterministic order and could potentially mark events as "consumed" causing them not to propagate to subsequent listeners.
• One can use the CopyOnWriteArrayList implementation, which allows a listener to remove itself during a notification callback without a ConcurrentModificationException being thrown (this is very important and is a classic gotcha when writing event oriented code).

这篇关于注册Java事件时，通常允许重复的侦听器？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！