問題描述

根據(jù)這些:

1. http://docs.oracle.com/javase/6/docs/api/java/util/HashMap.html
2. HashMap、LinkedHashMap和TreeMap的區(qū)別
3. java初學(xué)者:如何在hashmaps中對(duì)key進(jìn)行排序?

Java 中的 HashMap 應(yīng)該是未排序的，但它正在根據(jù) Key 進(jìn)行排序.

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

我遇到了這個(gè)問題，因?yàn)槲倚枰迦胗唵螖?shù)據(jù).所以，我使用 LinkedHashMap 代替.但是我仍然很困惑為什么 HashMap 對(duì)其進(jìn)行排序.

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.

誰能解釋一下?

我做了一個(gè)簡(jiǎn)單的例子來查看排序.

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();
        }

    }

結(jié)果:

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

我嘗試使用 Java 的 Random 插入 50 個(gè)隨機(jī)數(shù)，但發(fā)現(xiàn)一些數(shù)據(jù)未排序.但是，它仍然能夠?qū)Υ蠖鄶?shù)整數(shù)進(jìn)行排序.

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.

隨機(jī)結(jié)果:

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

推薦答案

這是巧合(不是真的，而是與哈希算法有關(guān)).

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

嘗試添加

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

最后一次.

輸出將是

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

javadoc 具體說

The javadoc specifically says

這個(gè)類不保證地圖的順序；特別是，它不保證訂單會(huì)隨著時(shí)間的推移保持不變.

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.

這篇關(guān)于HashMap 應(yīng)該是未排序的，但仍然根據(jù) key 排序的文章就介紹到這了，希望我們推薦的答案對(duì)大家有所幫助，也希望大家多多支持html5模板網(wǎng)！