java函数定义与对象创建

Question

在下面的代码中，我想了解 Collections.sort 函数在做什么。这意味着什么

Collections.sort(list, new Comparator() { a complete java function });

我明白new Comparator()意味着一个类对象，但是这里的功能 block 的用途是什么，以及我们在java中如何调用它。

谢谢。

/**
     * Sorts/shuffles the given list according to the current sending queue 
     * mode. The list can contain either Message or Tuple<Message, Connection> 
     * objects. Other objects cause error. 
     * @param list The list to sort or shuffle
     * @return The sorted/shuffled list
     */
    @SuppressWarnings(value = "unchecked") /* ugly way to make this generic */
    protected List sortByQueueMode(List list) {
        switch (sendQueueMode) {

    case Q_MODE_RANDOM:
        Collections.shuffle(list, new Random(SimClock.getIntTime()));
        break;
    case Q_MODE_FIFO:
        Collections.sort(list, 
                new Comparator() {
            /** Compares two tuples by their messages' receiving time */
            public int compare(Object o1, Object o2) {
                double diff;
                Message m1, m2;

                if (o1 instanceof Tuple) {
                    m1 = ((Tuple<Message, Connection>)o1).getKey();
                    m2 = ((Tuple<Message, Connection>)o2).getKey();
                }
                else if (o1 instanceof Message) {
                    m1 = (Message)o1;
                    m2 = (Message)o2;
                }
                else {
                    throw new SimError("Invalid type of objects in " + 
                            "the list");
                }

                diff = m1.getReceiveTime() - m2.getReceiveTime();
                if (diff == 0) {
                    return 0;
                }
                return (diff < 0 ? -1 : 1);
            }
        });
        break;
    /* add more queue modes here */
    default:
        throw new SimError("Unknown queue mode " + sendQueueMode);
    }

    return list;
}

我终于了解了比较器。这个简单的例子会有所帮助:

 Collections.sort(ls, new Comparator() 
                           {

                            public int compare(Object o1, Object o2) 
                            {
                            String sa = (String)o1;
                            String sb = (String)o2;

                            int v = sa.compareTo(sb);

                            return v;           

                                // it can also return 0, and 1
                            }
                           }    
                    );

Answer 1

这就是 anonymous inner class .
它用于将函数作为参数传递，因为 Java 不支持函数指针。