java - 为集合循环

Question

我有以下代码:

LinkedHashMap<String,ArrayList<String>> h;
Set set = h.entrySet();     
Iterator i = set.iterator();
        while(i.hasNext()) {
            System.out.println(i.next());
            Map.Entry me = (Map.Entry)i.next();
            String currentSegString = (String) me.getKey();

            System.out.println(currentKey+"**************");
        }

打印出这个:

1=[]
2**************
3=[A, B, C]
4**************
5=[]

但随后我删除了一行 System.out.println(i.next());:

LinkedHashMap<String,ArrayList<String>> h;
Set set = h.entrySet();     
Iterator i = set.iterator();
        while(i.hasNext()) {

            Map.Entry me = (Map.Entry)i.next();
            String currentSegString = (String) me.getKey();

            System.out.println(currentKey+"**************");
        }

它打印出这个:

1**************
2**************
3**************
4**************
5**************

为什么在第一种情况下每个键不打印 ****************？

Answer 1

那是因为当你这样做时:

System.out.println(i.next());

您将跳到下一行，然后 Map 也会执行 .next()

因此您只能看到可能的 5 行中的 2 行。

说明:

     while(i.hasNext()) { 
        System.out.println(i.next()); //skip one  #1, #3, #5
        Map.Entry me = (Map.Entry)i.next(); //goto next one #2, #4
        String currentSegString = (String) me.getKey();

        System.out.println(currentKey+"**************"); //output #2,4
    }

第二个代码:

    while(i.hasNext()) {

        Map.Entry me = (Map.Entry)i.next(); //goto next one #1, #2, #3, #4, #5
        String currentSegString = (String) me.getKey();

        System.out.println(currentKey+"**************"); //output #1,2,3,4,5
    }

解决这个问题的方法是:

    while(i.hasNext()) {
        Object temp = i.next(); //goto next one #1, #2, #3, #4, #5
        System.out.println(temp);
        Map.Entry me = (Map.Entry)temp; 
        String currentSegString = (String) me.getKey();

        System.out.println(currentKey+"**************"); //output #1,2,3,4,5
    }