在实际业务开发中，可能会遇到Java Map按值排序的需要。
Java Map按值排序的常见思路是：
1、 将map中的entry放到List中
2、 对List中的entry通过比较器按值排序
3 、将排序后的entry放到linkedhashmap中
Java 8利用Stream
代码语言：javascript复制import java.util.Collections;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.Map;
import static java.util.Map.Entry.comparingByValue;
import static java.util.stream.Collectors.toMap;
public class SortTest {
public static void main(String[] args) throws Exception {
// 创建一个字符串为Key，数字为值的map
Map budget = new HashMap<>();
budget.put("clothes", 120);
budget.put("grocery", 150);
budget.put("transportation", 100);
budget.put("utility", 130);
budget.put("rent", 1150);
budget.put("miscellneous", 90);
System.out.println("排序前: " budget);
// 按值排序 升序
Map sorted = budget
.entrySet()
.stream()
.sorted(comparingByValue())
.collect(
toMap(Map.Entry::getKey, Map.Entry::getValue, (e1, e2) -> e2,
LinkedHashMap::new));
System.out.println("升序按值排序后的map: " sorted);
// 按值排序降序
sorted = budget
.entrySet()
.stream()
.sorted(Collections.reverseOrder(comparingByValue()))
.collect(
toMap(Map.Entry::getKey, Map.Entry::getValue, (e1, e2) -> e2,
LinkedHashMap::new));
System.out.println("降序按值排序后的map: " sorted);
}
}可以封装成工具类
代码语言：javascript复制/**
* Map排序工具类
*
* @author liuwangyanghdu@163.com 明明如月
*/
public class MapSortUtil {
private static Comparator comparatorByKeyAsc = (Map.Entry o1, Map.Entry o2) -> {
if (o1.getKey() instanceof Comparable) {
return ((Comparable) o1.getKey()).compareTo(o2.getKey());
}
throw new UnsupportedOperationException("键的类型尚未实现Comparable接口");
};
private static Comparator comparatorByKeyDesc = (Map.Entry o1, Map.Entry o2) -> {
if (o1.getKey() instanceof Comparable) {
return ((Comparable) o2.getKey()).compareTo(o1.getKey());
}
throw new UnsupportedOperationException("键的类型尚未实现Comparable接口");
};
private static Comparator comparatorByValueAsc = (Map.Entry o1, Map.Entry o2) -> {
if (o1.getValue() instanceof Comparable) {
return ((Comparable) o1.getValue()).compareTo(o2.getValue());
}
throw new UnsupportedOperationException("值的类型尚未实现Comparable接口");
};
private static Comparator comparatorByValueDesc = (Map.Entry o1, Map.Entry o2) -> {
if (o1.getValue() instanceof Comparable) {
return ((Comparable) o2.getValue()).compareTo(o1.getValue());
}
throw new UnsupportedOperationException("值的类型尚未实现Comparable接口");
};
/**
* 按键升序排列
*/
public static Map sortByKeyAsc(Map originMap) {
if (originMap == null) {
return null;
}
return sort(originMap, comparatorByKeyAsc);
}
/**
* 按键降序排列
*/
public static Map sortByKeyDesc(Map originMap) {
if (originMap == null) {
return null;
}
return sort(originMap, comparatorByKeyDesc);
}
/**
* 按值升序排列
*/
public static Map sortByValueAsc(Map originMap) {
if (originMap == null) {
return null;
}
return sort(originMap, comparatorByValueAsc);
}
/**
* 按值降序排列
*/
public static Map sortByValueDesc(Map originMap) {
if (originMap == null) {
return null;
}
return sort(originMap, comparatorByValueDesc);
}
private static Map sort(Map originMap, Comparator comparator) {
return originMap.entrySet()
.stream()
.sorted(comparator)
.collect(
Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (e1, e2) -> e2,
LinkedHashMap::new));
}
}测试类
代码语言：javascript复制package com.chujianyun.common.map;
import org.junit.jupiter.api.BeforeAll;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.TestInstance;
import java.util.HashMap;
import java.util.Map;
/**
* Map排序工具类
*
* @author liuwangyanghdu@163.com 明明如月
*/
@TestInstance(TestInstance.Lifecycle.PER_CLASS)
class MapSortUtilTest {
// 创建一个字符串为Key，数字为值的map
Map budget = new HashMap<>();
@BeforeAll
public void init() {
budget.put("clothes", 120);
budget.put("grocery", 150);
budget.put("transportation", 100);
budget.put("utility", 130);
budget.put("rent", 1150);
budget.put("miscellneous", 90);
System.out.println("排序前: " budget);
}
@Test
void sortByKeyAsc() {
System.out.println("按键升序" MapSortUtil.sortByKeyAsc(budget));
}
@Test
void sortByKeyDesc() {
System.out.println("按键降序" MapSortUtil.sortByKeyDesc(budget));
}
@Test
void sortByValueAsc() {
System.out.println("按值升序" MapSortUtil.sortByValueAsc(budget));
}
@Test
void sortByValueDesc() {
System.out.println("按值降序" MapSortUtil.sortByValueDesc(budget));
}
}Java 7版本
代码语言：javascript复制import java.util.*;
import java.lang.*;
public class GFG {
// hashmap按值排序
public static HashMap sortByValue(HashMap hm)
{
// HashMap的entry放到List中
List > list =
new LinkedList >(hm.entrySet());
// 对List按entry的value排序
Collections.sort(list, new Comparator >() {
public int compare(Map.Entry o1,
Map.Entry o2)
{
return (o1.getValue()).compareTo(o2.getValue());
}
});
// 将排序后的元素放到LinkedHashMap中
HashMap temp = new LinkedHashMap();
for (Map.Entry aa : list) {
temp.put(aa.getKey(), aa.getValue());
}
return temp;
}
public static void main(String[] args)
{
HashMap hm = new HashMap();
// 填充测试数据
hm.put("Math", 98);
hm.put("Data Structure", 85);
hm.put("Database", 91);
hm.put("Java", 95);
hm.put("Operating System", 79);
hm.put("Networking", 80);
Map hm1 = sortByValue(hm);
// 打印按值排序后的数据
for (Map.Entry en : hm1.entrySet()) {
System.out.println("Key = " en.getKey()
", Value = " en.getValue());
}
}
} 参考文章：
1、 Java 8 – Sorting HashMap by values in ascending and descending order
2、 Sort a Map by values
3、Sorting a Hashmap according to values
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