JDK中此代码的用途是什么？

Question

以下代码取自Oracle jdk1.8.0_40 AbstractListModel类.

   /**
     * <code>AbstractListModel</code> subclasses must call this method
     * <b>after</b>
     * one or more elements of the list change.  The changed elements
     * are specified by the closed interval index0, index1 -- the endpoints
     * are included.  Note that
     * index0 need not be less than or equal to index1.
     *
     * @param source the <code>ListModel</code> that changed, typically "this"
     * @param index0 one end of the new interval
     * @param index1 the other end of the new interval
     * @see EventListenerList
     * @see DefaultListModel
     */
    protected void fireContentsChanged(Object source, int index0, int index1)
    {
        Object[] listeners = listenerList.getListenerList();
        ListDataEvent e = null;

        for (int i = listeners.length - 2; i >= 0; i -= 2) {
            if (listeners[i] == ListDataListener.class) {
                if (e == null) {
                    e = new ListDataEvent(source, ListDataEvent.CONTENTS_CHANGED, index0, index1);
                }
                ((ListDataListener)listeners[i+1]).contentsChanged(e);
            }
        }
    }

我的问题是

• 为什么迭代开始在listeners.length - 2怎么样的listeners.length - 1元素？
• 为什么每个其他元素(i -= 2)触发事件？
• 为什么迭代的顺序相反？

也是openjdk中代码的链接.

Answer 1

该listeners数组包含Class偶数索引中的侦听器对象和奇数索引中的侦听器实例.

因此,循环检查listeners数组中每个偶数索引的类型

if (listeners[i] == ListDataListener.class

但仅针对奇数指数触发事件:

((ListDataListener)listeners[i+1]).contentsChanged(e);

listeners.length - 1没有被跳过.从什么时候开始i == listeners.length - 2,i+1 == listeners.length - 1.

我不确定逆序迭代的原因.