什么addActionListener方法呢？ [英] What addActionListener does?

问题描述

我有以下的code：

JButton button = new JButton("Clear");
button.addActionListener(this);

据我了解，我创建的，它是写清除按钮。然后，我必须用此按钮的动作（如按钮pressed会发生什么）相关联，它是由 addActionListener方法完成。是不是？

但我不明白的是指定的操作位置。按钮的preSS应该清除文本区域，而且据我了解，应该有一个地方code从而清除文本区域。但是，在给定的示例中，只有本中的参数在 addActionListener方法（）

But what I do not understand is where the action is specified. The press of the button should clear text area and, as far as I understand, there should be somewhere a code which clear the text area. But in the given example there is only "this" in the arguments of the addActionListener().

程序如何知道，当按钮pssed $ P $应该清除文本区域？

How the program knows that it should clear the text area when the button is pressed?

如果需要的话，满code给出<一个href=\"http://java.sun.com/docs/books/tutorial/uiswing/examples/events/KeyEventDemoProject/src/events/KeyEventDemo.java\"相对=nofollow>这里。

If it is needed, the full code is given here.

推荐答案

这是<一个href=\"http://java.sun.com/javase/6/docs/api/java/awt/event/ActionListener.html\"><$c$c>ActionListener是一个回调的机制。当它被添加到火灾的的ActionEvent 的公共无效的actionPerformed（ActionEvent的五）方法将被调用的控制。

An ActionListener is a callback mechanism. Whenever a control it is added to fires an ActionEvent, the public void actionPerformed(ActionEvent e) method will be invoked.

我不明白的是，其中的actionPerformed被调用。我看到它是在类中定义但没有地方调用此方法。

What I do not understand is where the actionPerformed is called. I see that it is defined within the class but there is no place where this method is called.

这是由UI组件的内部机制调用。从概念上讲，你能想到的code的看起来有点像这样：

This is called by the internal mechanisms of the UI component. Conceptually, you can think of the code looking a bit like this:

public class Button {
  private final List<ActionListener> listeners = new ArrayList<ActionListener>();

  public void addActionListener(ActionListener l) {
    listeners.add(l);
  }

  public void click() {
    ActionEvent event = new ActionEvent(this, 0, "click");
    for (ActionListener l : listeners) {
      l.actionPerformed(event);
    }
  }
}

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