HashMap应该是未排序的，但仍然按照键排序 [英] HashMap should be unsorted but still sorts according to key

问题描述

根据这些：

1. http://docs.oracle.com/javase/6/docs/api/java/util/HashMap.html


2. Java中的HashMap，LinkedHashMap和SortedMap之间的区别


3. java初学者：如何在hashmaps中按键进行排序？

1. http://docs.oracle.com/javase/6/docs/api/java/util/HashMap.html
2. Difference between HashMap, LinkedHashMap and SortedMap in Java
3. java beginner : How key gets sorted in hashmaps?

HashMap 在 Java 应该是未排序的，但是它正在被排序关于 Key 。

The HashMap in Java should be unsorted but it is being sorted with respect to Key.

我遇到这个问题，因为我需要插入订单数据。所以，我使用了 LinkedHashMap 。但是我仍然很困惑，为什么 HashMap 将它排序。

I experienced this as a problem because I needed inserted-order data. So, I used LinkedHashMap instead. But still I am confused why the HashMap sorted it.

有人可以解释吗？

我做了一个简单的例子来查看排序。

I did a simple example to view the sort.

public static void main(String[] args) {

        HashMap<Integer, String> newHashMap = new HashMap<Integer, String>();
        newHashMap.put(2, "First");
        newHashMap.put(0, "Second");
        newHashMap.put(3, "Third");
        newHashMap.put(1, "Fourth");

        Iterator<Entry<Integer, String>> iterator = newHashMap.entrySet()
                .iterator();
        while (iterator.hasNext()) {

            Map.Entry<Integer, String> entry = iterator.next();
            System.out.println("Key: " + entry.getKey());
            System.out.println("Value: " + entry.getValue());
            iterator.remove();
        }

    }

结果： strong>

Result:

Key: 0
Value: Second
Key: 1
Value: Fourth
Key: 2
Value: First
Key: 3
Value: Third

编辑：

我试图使用随机 Java ，我发现一些数据未排序。但是，它仍然设法排序大部分的整数。

I tried to insert 50 random numbers using Random of Java and I found some data unsorted. But, it still manages to sort most of the integers.

随机结果：

...
Key: 36
Value: random
Key: 43
Value: random
Key: 47
Value: random
Key: 44
Value: random
Key: 45
Value: random
...

推荐答案

这是巧合（不是真的，而是与散列算法有关）。

It's a coincidence (not really, rather it has to do with the hashing algorithm).

尝试添加

newHashMap.put(-5, "Fifth");

as last。

输出将

Key: 0
Value: Second
Key: 1
Value: Fourth
Key: 2
Value: First
Key: 3
Value: Third
Key: -5
Value: Fifth

javadoc具体说

The javadoc specifically says

关于地图顺序的保证;特别是，它不能保证订单在一段时间内保持不变。

This class makes no guarantees as to the order of the map; in particular, it does not guarantee that the order will remain constant over time.

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