降序排序:Java Map [英] Sorting Descending order: Java Map

问题描述

我想做的是按值对地图进行排序.我查看了 stackoverflow 网站上提供的许多问题，并发现以下解决方案可以满足我的需求，但缺少一个小东西.

What I want to do is sort a map by value. I went over many questions that are available on the stackoverflow site and found out following solution that does what I want but missing a small thing.

Link1:排序图

但我遇到的问题是，默认情况下这是按值升序排序的.我想按降序排列:

But the issue I am running into is that by default this is sorted by ascending order by value. I want to order it by descending order:

所以我所做的是我创建了一个实现比较器的类

So what I did was I created a class that implements a comparator

class MyComparator implements Comparator {
    Map map;
    public MyComparator(Map map) {
        this.map = map;
    }
    public int compare(Object o1, Object o2) {
        return ((Integer) map.get(o2)).compareTo((Integer) map.get(o1));
    }
}

然后我将我的地图传递给树形图，

And then I pass my map to the treemap,

MyComparator comp = new MyComparator(myMap);
Map<String, Integer> newMap = new TreeMap(comp);
newMap.putAll(myMap);

这似乎是一种不好的方法，因为我觉得这效率低下.有没有办法将链接中的解决方案更改为默认按降序排序.

This seems like bad approach because I feel this is inefficient. Is there a way to change the solution in the link to do ordering on descending order by default.

推荐答案

你应该使用 new TreeMap<>(Collections.reverseOrder());.

Map<String, Integer> newMap = new TreeMap<>(Collections.reverseOrder());
newMap.putAll(myMap);

或反转现有的比较器，如值比较器 Collections.reverseOrder(comparator).它的工作方式类似于您在调用 compare/compareTo 之前交换两个对象的方法.

or to reverse an existing comparator like the value-comparator Collections.reverseOrder(comparator). It works like your approach swapping the two objects before invoking compare/compareTo.

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