如何从Java Map获取元素位置 [英] How to get element position from Java Map

问题描述

我有这张Java地图：

I have this Java Map:

你能告诉我如何获得地图的第6个元素吗？

Can you tell me how I can get the 6-th element of the Map?

private static final Map<String, Users> cache = new HashMap<>();

这可能吗？或者我必须使用另一个Java集合？

is this possible? Or I have to use another Java collection?

推荐答案

虽然回答有点迟。但是可以选择使用 LinkedHashMap ：这个地图根据元素的插入保留了顺序，正如大家所建议的那样。但是，作为警告，它有一个构造函数 LinkedHashMap（int initialCapacity，float loadFactor，boolean accessOrder），它将创建一个链接的哈希映射，其迭代顺序是其中的顺序它的条目是最后访问。在这种情况下不要使用这个构造函数。

Though a bit late to answer. But the option is to use LinkedHashMap: this map preserves the order according to insertion of elements, as everyone has suggested. However, As a warning, it has a constructor LinkedHashMap(int initialCapacity, float loadFactor, boolean accessOrder) which will create a linked hash map whose order of iteration is the order in which its entries were last accessed. Don't use this constructor for this case.

但是，如果我需要这样的功能，我会扩展它并实现我的必要功能，以OOP方式重用它们。

However, if I needed such functionality, i would extend it and implement my necessary function to re-use them in OOP way.

class MyLinkedMap<K, V> extends LinkedHashMap<K, V>
{

    public V getValue(int i)
    {

       Map.Entry<K, V>entry = this.getEntry(i);
       if(entry == null) return null;

       return entry.getValue();
    }

    public Map.Entry<K, V> getEntry(int i)
    {
        // check if negetive index provided
        Set<Map.Entry<K,V>>entries = entrySet();
        int j = 0;

        for(Map.Entry<K, V>entry : entries)
            if(j++ == i)return entry;

        return null;

    }

}

现在我可以实例化它并可以获得我想要的条目和值：

Now i can instantiate it and can get a entry and value either way i want:

MyLinkedMap<String, Integer>map = new MyLinkedMap<>();
map.put("a first", 1);
map.put("a second", 2);
map.put("a third", 3);

System.out.println(map.getValue(2));
System.out.println(map.getEntry(1)); 

输出：

3
a second=2

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