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Java 8 Map sort

java8 来源:最后的miku殿下 3次浏览

Java 8 Map 排序

Java 8的Stream例子Map,按键或按值排序

快速说明

在Java 8中排序地图的步骤

  1. 将map转换为流
  2. 排序
  3. Collect and return 新的LinkedHashMap
Map result = map.entrySet().stream() .sorted(Map.Entry.comparingByKey()) .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (oldValue, newValue) -> oldValue, LinkedHashMap::new));

默认情况下Collectors.toMap会返回一个HashMap


2.按键排序
SortByKeyExample.java

package com.mkyong.test;  import java.util.HashMap; import java.util.LinkedHashMap; import java.util.Map; import java.util.stream.Collectors;  public class SortByKeyExample {   public static void main(String[] argv) {   Map<String, Integer> unsortMap = new HashMap<>(); unsortMap.put("z", 10); unsortMap.put("b", 5); unsortMap.put("a", 6); unsortMap.put("c", 20); unsortMap.put("d", 1); unsortMap.put("e", 7); unsortMap.put("y", 8); unsortMap.put("n", 99); unsortMap.put("g", 50); unsortMap.put("m", 2); unsortMap.put("f", 9);  System.out.println("Original..."); System.out.println(unsortMap);  // sort by keys, a,b,c..., and return a new LinkedHashMap // toMap() will returns HashMap by default, we need LinkedHashMap to keep the order. Map<String, Integer> result = unsortMap.entrySet().stream() .sorted(Map.Entry.comparingByKey()) .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (oldValue, newValue) -> oldValue, LinkedHashMap::new));   // Not Recommend, but it works. //Alternative way to sort a Map by keys, and put it into the "result" map Map<String, Integer> result2 = new LinkedHashMap<>(); unsortMap.entrySet().stream() .sorted(Map.Entry.comparingByKey()) .forEachOrdered(x -> result2.put(x.getKey(), x.getValue()));  System.out.println("Sorted..."); System.out.println(result); System.out.println(result2);  }  }

Output

原版的...
{a = 6,b = 5,c = 20,d = 1,e = 7,f = 9,g = 50,y = 8,z = 10,m = 2,n = 99}

排序...
{a = 6,b = 5,c = 20,d = 1,e = 7,f = 9,g = 50,m = 2,n = 99,y = 8,z = 10}
{a = 6,b = 5,c = 20,d = 1,e = 7,f = 9,g = 50,m = 2,n = 99,y = 8,z = 10}

3.按值排序

SortByValueExample.java

package com.mkyong.test;  package com.mkyong;  import java.util.Comparator; import java.util.HashMap; import java.util.LinkedHashMap; import java.util.Map; import java.util.stream.Collectors;  public class SortByValueExample {   public static void main(String[] argv) {   Map<String, Integer> unsortMap = new HashMap<>(); unsortMap.put("z", 10); unsortMap.put("b", 5); unsortMap.put("a", 6); unsortMap.put("c", 20); unsortMap.put("d", 1); unsortMap.put("e", 7); unsortMap.put("y", 8); unsortMap.put("n", 99); unsortMap.put("g", 50); unsortMap.put("m", 2); unsortMap.put("f", 9);  System.out.println("Original..."); System.out.println(unsortMap);  //sort by values, and reserve it, 10,9,8,7,6... Map<String, Integer> result = unsortMap.entrySet().stream() .sorted(Map.Entry.comparingByValue(Comparator.reverseOrder())) .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (oldValue, newValue) -> oldValue, LinkedHashMap::new));   //Alternative way Map<String, Integer> result2 = new LinkedHashMap<>(); unsortMap.entrySet().stream() .sorted(Map.Entry.<String, Integer>comparingByValue().reversed()) .forEachOrdered(x -> result2.put(x.getKey(), x.getValue()));  System.out.println("Sorted..."); System.out.println(result); System.out.println(result2);  } }

Output

原版的...
{a = 6,b = 5,c = 20,d = 1,e = 7,f = 9,g = 50,y = 8,z = 10,m = 2,n = 99}

排序...
{n = 99,g = 50,c = 20,z = 10,f = 9,y = 8,e = 7,a = 6,b = 5,m = 2,d = 1}
{n = 99,g = 50,c = 20,z = 10,f = 9,y = 8,e = 7,a = 6,b = 5,m = 2,d = 1}


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