如何使 HashMap 与自定义键类型一起正常工作?

How to make HashMap work properly with custom key type?(如何使 HashMap 与自定义键类型一起正常工作?)

问题描述

我认为我的问题很简单，但是我找不到解决方案，所以我决定在这里提问.我需要的是用这样的自定义键类型制作一个 HashMap:

I think my question is quite simple, however I couldn't find the solution so I decided to ask here. What i need is to make a HashMap with a custom Key type like this:

HashMap<Pair<Integer, Integer>, StrategyPoint> myMap = new HashMap<Pair<Integer, Integer>, StrategyPoint> ();

但是我在这里遗漏了一些东西，因为 HashMap 停止正常工作.首先，Key 变得不唯一，并且可以在 keySet 中找到具有相同值的不同 Pair 实例.包含键功能也不能像我想象的那样工作:).

However I am missing something here, because the HashMap stops working properly. First the Key becomes not unique and a different instances of Pair with same values can be found in the keySet. Also the contains key function does not work the way I suppose it to :).

我显然错过了一些东西，更有可能我应该以某种方式定义一种方法来比较我的 Pair 类中的实例.但是，我尝试在我的 Pair 类中使用 compareTo 实现 Comparable，但它仍然无法正常工作.有什么建议吗?

I clearly miss something and more likely I should somehow define a way to compare my instances from my Pair class. However I tried implementing Comparable with compareTo in my Pair class and it still don't work. Any suggestions?

我的原始代码有点凌乱且不友好，所以我在这里做了一个例子来说明我的问题.

My original code is kinda messy and unfriendly to read, so I made an example just to illustrate my problem here.

代码如下:

HashMap<Pair<Integer, Integer>, StrategyPoint> myMap = new HashMap<Pair<Integer, Integer>, StrategyPoint> ();
    Pair<Integer, Integer> myPair = new Pair<Integer, Integer>(2,2);
    StrategyPoint myPoint= new StrategyPoint(2, 2, 5, 5, false);
    myMap.put(myPair, myPoint);


    Pair<Integer, Integer> searcher = new Pair<Integer, Integer> (0,0);
    searcher.setFirst(2);
    searcher.setSecond(2);
    System.out.println(myMap.containsKey(searcher));
    System.out.println(myMap.containsKey(myPair));

执行的结果是:

false

true

我已经对其进行了调试，并且搜索器实例已正确填充，但是 HashMap 似乎拒绝在其 keySet 中找到它.

I have debug it and the searcher instance is being populated properly, however it seems the HashMap refuse to find it in its keySet.

推荐答案

您必须在 Pair 类上正确实现 equals 和 hashCode.

You must implement properly equals and hashCode on the Pair class.

HashMap 使用这些方法来区分和散列键类.

The HashMap uses these methods to differentiate and hash the key class.

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