java - 按值的降序对 Map 进行排序

Question

我一直在尝试按 values 的降序对 map 进行排序但我现有的代码按 keys 降序排序。如何按值的降序排序？ 我的代码:

System.out.println("Unsorted Map:" +merger);
Map<Integer, Double> Sortedmerger = SortByValue(merger); 
System.out.println("Sorted Map: "+ Sortedmerger);

public static TreeMap<Integer, Double> SortByValue  (Map<Integer, Double> map) {
ValueComparator vc =  new ValueComparator(map);
TreeMap<Integer, Double> sortedMap = new TreeMap<Integer, Double>(Collections.reverseOrder());
        sortedMap.putAll(map);
        return sortedMap;
    }   

class ValueComparator implements Comparator<Double> {

    Map<Integer, Double> map;

    public ValueComparator(Map<Integer, Double> base) {
        this.map = base;
    }

    public int compare(Double a, Double b) {
        if (map.get(a) >= map.get(b)) {
            return -1;
        } else {
            return 1;
        } // returning 0 would merge keys 
    }
}

我的输出:

Unsorted Map:{1=0.53, 2=0.48, 23=0.54, 10=0.47}
Sorted Map: {23=0.54, 10=0.47, 2=0.48, 1=0.53}

Answer 1

您的 map 键类型是整数，因此您必须使用 Comparator<Integer>和你的compare方法应该采用整数输入，通过该 Integer 键，您可以通过 map.get(a) 获得 Double 值和map.get(b) 。并在 TreeMap您必须定义您创建的比较器类的构造函数。(即 ValueComparator)

引用这段代码:

public static TreeMap<Integer, Double> SortByValue(Map<Integer, Double> map) {
        ValueComparator vc =  new ValueComparator(map);
        TreeMap<Integer, Double> sortedMap = new TreeMap<Integer, Double>(vc);\\constructor should be vc which extends Comparator
        sortedMap.putAll(map); 
        return sortedMap;
    }

class ValueComparator implements Comparator<Integer> {

    Map<Integer, Double> map;

    public ValueComparator(Map<Integer, Double> base) {
        this.map = base;
    }

    @Override
    public int compare(Integer a, Integer b) {
        // TODO Auto-generated method stub
        if (map.get(a) >= map.get(b)) {
            return -1;
        } else {
            return 1;
        }
    }
}