Java中监听器的目的是什么？ [英] What is the purpose of a listener in Java?

问题描述

我在网上找了这个，但找不到它究竟是什么的充分解释。我看到的是一个Java接口，它作为参数在另一个类中作为监听器传递。人们将各种监听器添加到列表中，并通过单个方法调用它们。

I looked for this online, but couldn't find an adequate explanation to what it exactly does. What I saw was a Java Interface and it was passed as a parameter in another class as a "Listener". People added various listeners to a list and called them all through a single method.

我不知道为什么要使用它。有人可以解释吗？

I'm not sure why I would use it. Can someone care to explain?

这是我原来的帮助帖子，有人告诉我使用听众。

This is my original help post where someone told me to use listeners.

链接

推荐答案

在链接 KillMonsterEventListener

public interface KillMonsterEventListener {
    void onKillMonster ();
}

为您的API用户提供了一种告诉您这样的方式：

provides a way for users of your API to tell you something like this:

这是一段代码。当一个怪物被杀死时，请回电话。我将决定该怎么做。

Here is a piece of code. When a monster is killed, call it back. I will decide what to do.

这是我在执行流中的特定点插入代码的一种方式（特别是在怪物被杀的时候）。我可以这样做：

This is a way for me to plug in my code at a specific point in your execution stream (specifically, at the point when a monster is killed). I can do something like this:

yourClass.addKillMonsterEventListener(
    new KillMonsterEventListener() {
        public onKillMonster() {
            System.out.println("A good monster is a dead monster!");
        }
    }
);

在其他地方我可以添加另一个听众：

Somewhere else I could add another listener:

yourClass.addKillMonsterEventListener(
    new KillMonsterEventListener() {
        public onKillMonster() {
            monsterCount--;
        }
    }
);

当您的代码通过杀死怪物的听众列表时，即

When your code goes through the list of listeners on killing a monster, i.e.

for (KillMonsterEventListener listener : listeners) {
    listener.onKillMonster()
}

我的代码片段（即 monsterCount - 和打印输出）都被执行了。关于它的好处是你的代码与我的代码完全分离：它不知道我在打印什么，我正在减少什么变量，等等。

both my code snippets (i.e. the monsterCount-- and the printout) get executed. The nice thing about it is that your code is completely decoupled from mine: it has no idea what I am printing, what variable I am decrementing, and so on.

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