java - HashMap get(key) 方法仅返回最后一个条目

Question

所以我百分百不知道是什么导致了这样的事情。这是我正在使用的整个代码部分

public static void getBestHeuristic(int[] nextParent) {

    int bestHeuristic = 0;

    Random rndm = new Random();
    int randomIndex = 0;
    HashMap<Integer, int[]> childHuristics = new HashMap<Integer, int[]>();
    int k = 0;
    while (k < nextParent.length - 1) {
        for (int i = 0; i < (nextParent.length) - 2; i++) {
            randomIndex = rndm.nextInt(nextParent.length / 5) + i;
            int temp = nextParent[i];
            nextParent[i] = nextParent[randomIndex];
            nextParent[randomIndex] = temp;
        }
        // Assign this random set to the child
        int[] childArray = nextParent;

        int childDistance = 0;

        // Calculate the heuristic of the new current child
        for (int j = 0; j < childArray.length - 1; j++) {
            childDistance += cities[childArray[j]][childArray[j + 1]];
        }

        childHuristics.put(childDistance, childArray);

        // Display the current values added to the HashMap
        System.out.println("Distance: " + childDistance);
        System.out.println(Arrays.toString(childArray));
        System.out.println();

        // Keep track of the lowest value
        if (bestHeuristic == 0) {
            bestHeuristic = childDistance;
        } else if (childDistance < bestHeuristic) {
            bestHeuristic = childDistance;
        }

        k++;
    }
    // Display the lowest distance
    System.out.println();
    System.out.println("The best child was: ");
    System.out.println("Distance: " + bestHeuristic);
    System.out.println(Arrays.toString(childHuristics.get(bestHeuristic)));

这是我从中得到的输出:

Distance: 670
[12, 5, 6, 10, 2, 3, 4, 8, 0, 9, 7, 1, 14, 11, 13]

Distance: 680
[6, 10, 2, 12, 4, 8, 5, 0, 9, 7, 3, 14, 13, 11, 1]

Distance: 611
[2, 12, 6, 4, 5, 8, 9, 7, 0, 10, 3, 13, 14, 11, 1]

Distance: 668
[2, 4, 5, 12, 9, 7, 6, 0, 3, 13, 10, 8, 14, 11, 1]

Distance: 684
[2, 5, 9, 7, 6, 12, 4, 13, 3, 8, 0, 14, 10, 11, 1]

Distance: 634
[2, 9, 5, 12, 6, 7, 4, 8, 3, 14, 0, 11, 13, 10, 1]

Distance: 736
[9, 12, 6, 7, 2, 8, 5, 4, 3, 11, 14, 13, 0, 10, 1]

Distance: 622
[9, 7, 6, 12, 5, 4, 3, 11, 8, 14, 0, 10, 1, 13, 2]

Distance: 585
[9, 7, 5, 6, 4, 11, 3, 12, 8, 0, 10, 13, 14, 1, 2]

Distance: 554
[9, 5, 7, 4, 6, 11, 8, 12, 3, 10, 0, 14, 13, 1, 2]

Distance: 587
[9, 7, 4, 6, 11, 5, 8, 3, 12, 0, 10, 1, 13, 14, 2]

Distance: 575
[7, 4, 6, 11, 8, 9, 5, 12, 3, 1, 0, 10, 14, 13, 2]

Distance: 642
[4, 6, 7, 8, 5, 12, 9, 3, 1, 0, 11, 14, 10, 13, 2]

Distance: 634
[4, 6, 7, 5, 9, 12, 1, 8, 0, 11, 10, 13, 14, 3, 2]


The best child was: 
Distance: 554
[4, 6, 7, 5, 9, 12, 1, 8, 0, 11, 10, 13, 14, 3, 2]

为了给所有这些提供一些上下文，基本上每个数组中的每个数字都有一个与之关联的距离值。这就是每个距离值所代表的意思。“cities”数组是保存所有这些距离值的二维数组。它看起来像这样:

0  29  82  46  68  52  72  42  51  55  29  74  23  72  46  
29   0  55  46  42  43  43  23  23  31  41  51  11  52  21  
82  55   0  68  46  55  23  43  41  29  79  21  64  31  51  
46  46  68   0  82  15  72  31  62  42  21  51  51  43  64  
68  42  46  82   0  74  23  52  21  46  82  58  46  65  23  
52  43  55  15  74   0  61  23  55  31  33  37  51  29  59  
72  43  23  72  23  61   0  42  23  31  77  37  51  46  33  
42  23  43  31  52  23  42  0  33   15  37  33  33  31  37  
51  23  41  62  21  55  23  33   0  29  62  46  29  51  11  
55  31  29  42  46  31  31  15  29   0  51  21  41  23  37  
29  41  79  21  82  33  77  37  62  51   0  65  42  59  61  
74  51  21  51  58  37  37  33  46  21  65   0  61  11  55  
23  11  64  51  46  51  51  33  29  41  42  61   0  62  23  
72  52  31  43  65  29  46  31  51  23  59  11  62   0  59  
46  21  51  64  23  59  33  37  11  37  61  55  23  59   0

我遇到的问题是，我拥有的 HashMap 的“get(key)”方法没有返回与我提供的键关联的数组。

它说 距离:554 [4、6、7、5、9、12、1、8、0、11、10、13、14、3、2]

当距离554实际排到这个数组时: [9、5、7、4、6、11、8、12、3、10、0、14、13、1、2]

我不知道我将它们放入 HashMap 的方式是否有问题。我尝试使用 TreeMap 强制对其进行排序并获取第一个值，但结果是相同的。

感谢您的宝贵时间。

Answer 1

这是因为您多次将相同的引用放入 map 中。如果你这样做

int[] childArray = nextParent.clone();

或

int[] childArray = Arrays.copyOf(nextParent, nextParent.length)

相反，您每次都会使用一个新的数组。