Java中Map排序方法及示例

import java.util.*;

public class Main {
public static void main(String[] args) {

// 创建一个新的TreeMap对象，并指定自然排序(默认为key的Comparable特性)
Map<String, Integer> sortedByKeys = new TreeMap<>();

// 添加一些元素到map中
sortedByKeys.put("Apple", 5);
sortedByKeys.put("Orange", 3);
sortedByKeys.put("Banana", 7);

System.out.println(sortedByKeys);
// 输出: {Apple=5, Banana=7, Orange=3}

// 如果要改变排序方式比如降序，可以通过Comparator构造函数初始化TreeMap：

Comparator<String> reverseOrderByKey = (k1, k2) -> -k1.compareTo(k2);

SortedMap<String,Integer> reversedSortMap = new TreeMap<>(reverseOrderByKey);

for(Map.Entry<String, Integer>e :sortedByKeys.entrySet()){
reversedSortMap.put(e.getKey(), e.getValue());
}

System.out.println(reversedSortMap);
// 输出: {Orange=3, Apple=5, Banana=7}

}

}

import java.util.*;
import java.util.stream.Collectors;

public class Main {

public static void main(String[] args) {

LinkedHashMap<Integer,String> linkedHashMap = new LinkedHashMap<>();

// 插入数据
linkedHashMap.put(4,"Pear");
linkedHashMap.put(6,"Grape");
linkedHashMap.put(2,"Strawberry");

// 默认行为就是维持insertion-order
Set<Map.Entry<Integer, String>> entriesOrderedByInsertion =
linkedHashMap.entrySet();

List<Map.Entry<Integer, String>> orderedList =
entriesOrderedByInsertion.stream()
.collect(Collectors.toList());

System.out.println(orderedList);
// 输出: [{2=Pear}, {4=Grape}, {6=Strawberry}]

// 若要使linkedhashmap依据value大小排序:

LinkedHashMap<Integer, String> valueSortedMap = new LinkedHashMap<>(
linkedHashMap.entrySet().stream()
..sorted(Map.Entry.comparingByValue())
.peek(e -> linkedHashMap.remove(e.getKey()))
.toArray(size -> new HashMap[size])
);

linkedHashMap.putAll(valueSortedMap);

System.out.println(linkedHashMap);
// 根据value排序后输出: {2=Strawberry, 4=Pear, 6=Grape}

}

}