排序功能提供不正确的结果

Question

我想priorities[]按降序排序,即...2,1,0.当我执行下面提供的代码时,我收到未排序的数组,例如

18, 14, 15, 19, 23, 37, 35, 1, 8, 24, 26, 36

为什么会这样？

double[] priorities = new double[10];
for (int i = 0; i < 10; i++) 
    priorities[i] = Math.round(10*Math.random();
ArrayIndexComparator comparator = new ArrayIndexComparator(priorities,1);
Integer[] sortedPriorities = comparator.createIndexArray();
Arrays.sort(sortedPriorities, comparator);


public class ArrayIndexComparator implements Comparator<Integer>
{
    private final double[] array;
    private int sort;

    public ArrayIndexComparator(double[] array, int sort)
    {
        this.array = array;
        this.sort = sort;
    }

    public Integer[] createIndexArray()
    {
        Integer[] indexes = new Integer[array.length];
        for (int i = 0; i < array.length; i++)
        {
            indexes[i] = i;
        }
        return indexes;
    }

    @Override
    public int compare(Integer index1, Integer index2)
    {
        if (sort == 0)
            return Double.compare(array[index2],array[index1]); // ascending order 0,1,2,...
        else
            return Double.compare(array[index1],array[index2]); // descending order ...2,1,0
    }
}

Answer 1

使用调试器会显示比较器不起作用的原因.好像你过分复杂了.所有比较器应该做的是采取两个元素,比较它们并返回一个满足您订购要求的结果.

你正在寻找一个有效地逆转双打的"自然"顺序的比较器,所以尝试一下以下方面:

double[] priorities = new double[10];
for (int i = 0; i < priorities.length; i++) 
    priorities[i] = Math.round(10*Math.random());
Arrays.sort(priorities, new ArrayIndexComparator());

...
...

public class ArrayIndexComparator implements Comparator<Double> {
    @Override
    public int compare(Double d1, Double d2) {
        return -1*d1.compareTo(d2);
    }
}

(简而言之.你应该真的ArrayIndexComparator变成一个单身人士,但这超出了这个问题的范围)

如果你太懒了,你可以下载Commons-Collections并使用内置的反向比较器:

Arrays.sort(priorities, ComparatorUtils.reversedComparator(
    ComparatorUtils.naturalComparator()));

然后你甚至不需要自己的自定义比较器类.