java - 为什么containsKey没有找到key？

Question

我有以下代码:

payoffs2exchanges.put(point, exchange);
if (!payoffs2exchanges.containsKey(point) ) {
   game.log.fine("yes");
} else {
   game.log.fine("no");
}

它输出“否”。换句话说，我将键值对添加到映射中，然后立即检查该键是否存在并发现它不存在。为什么？

我仍然对 key 有疑问。以下代码表示每次我添加一个 key 时我都会添加一个新 key 。我知道事实并非如此。

        Integer[] point = new Integer[2];
        point[0] = proposerBestScore;
        point[1] = responderBestScore;
        game.log.fine("In the getCloudOfPayoffs: found payoffs:" + point[0] + "," + point[1] + ". Exchange: " + exchange[0]+","+exchange[1]+","+exchange[2]+","+exchange[3]+","+exchange[4]);
        // With the following block we ensure that every options (pair of payoffs) is represented by exchange with minimal number of moves.
        if (!payoffs2exchanges.containsKey(point)) {
            payoffs2exchanges.put(point, exchange); 
            game.log.fine("In the getCloudOfPayoffs: this option is new. We add it to the map.");
        } else {
            game.log.fine("In the getCloudOfPayoffs: this option is old.");
            Integer[] exchangeFromMap = payoffs2exchanges.get(point);
            Integer newSum = 0;
            Integer oldSum = 0;
            for (int i=0;i<Design.nColors;i++) {
                newSum = newSum + Math.abs(exchange[i]);
                oldSum = oldSum + Math.abs(exchangeFromMap[i]);
            }
            if (newSum<oldSum) {
                game.log.fine("In the getCloudOfPayoffs: the new exchange is better than the old one.");
                payoffs2exchanges.put(point, exchange);
            }
        }

Answer 1

您正在使用 Integer[] 作为 map 中的键。这是一件坏事，因为 Java 数组没有像您预期的那样实现 equals 和 hashCode。请看这个例子:

public class Test {
    public static void main(String[] args) {
        Integer[] arr1 = { 1, 2 };
        Integer[] arr2 = { 1, 2 };

        System.out.println(arr1.equals(arr2));
        System.out.println(arr1.hashCode() + " / " + arr2.hashCode());
    }
}

在我的电脑上打印:

false
1476323068 / 535746438

我的建议是创建一个自定义的 Point 类，它可以正确地覆盖 equals 和 hashCode(或者可能重用 java.awt.如果您认为有道理，请点 。