排序降序：Java地图 [英] Sorting Descending order: Java Map

问题描述

我想要做的是按价值排序地图。我回顾了很多在stackoverflow站点上可用的问题，并发现了下面的解决方案，它可以做我想做的事情，但缺少一件小事。

Link1 ：Sorting Map

但是我遇到的问题是，默认情况下，这是按值升序排列的。我想按降序排列：

所以我做的是我创建了一个实现比较器的类

  class MyComparator实现比较器{
 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））; 
 
 
  

然后我将地图传递给树形图， / p>

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

这看起来很糟糕，因为我觉得这样做效率不高。有没有办法改变链接中的解决方案以默认降序排序。 >。

 地图< 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比较器）它的作用就像在调用 compare / compareTo <>之前交换两个对象。 / p>

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: Sorting Map

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:

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));
    }
}

And then I pass my map to the treemap,

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

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.

解决方案

You should use new TreeMap(Collections.reverseOrder());.

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

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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