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Java8 sort map by key or value

java 来源:Freeland丶 2次浏览

1. Sort by Key

SortByKeyExample.java

package com.mkyong.test; import java.util.HashMap; import java.util.LinkedHashMap; import java.util.Map; 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("j", 50); unsortMap.put("m", 2); unsortMap.put("f", 9); System.out.println("Original..."); System.out.println(unsortMap); Map<String, Integer> result = new LinkedHashMap<>(); //sort by key, a,b,c..., and put it into the "result" map unsortMap.entrySet().stream() .sorted(Map.Entry.<String, Integer>comparingByKey()) .forEachOrdered(x -> result.put(x.getKey(), x.getValue())); System.out.println("Sorted..."); System.out.println(result); } }

Output

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

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

2. Sort by Value SortByValueExample.java

package com.mkyong.test; import java.util.HashMap; import java.util.LinkedHashMap; import java.util.Map; 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("j", 50); unsortMap.put("m", 2); unsortMap.put("f", 9); System.out.println("Original..."); System.out.println(unsortMap); Map<String, Integer> result = new LinkedHashMap<>(); //sort by value, and reserve, 10,9,8,7,6... unsortMap.entrySet().stream() .sorted(Map.Entry.<String, Integer>comparingByValue().reversed()) .forEachOrdered(x -> result.put(x.getKey(), x.getValue())); System.out.println("Sorted..."); System.out.println(result); } }

Output

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

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

3. Generic Example

Create a generic method to sort a Map.

SortByGenericExample.java

package com.mkyong.test; import java.util.HashMap; import java.util.LinkedHashMap; import java.util.Map; import java.util.stream.Stream; public class SortByGenericExample {  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("j", 50); unsortMap.put("m", 2); unsortMap.put("f", 9); System.out.println("Original..."); System.out.println(unsortMap); System.out.println("Sort By Key..."); Map<String, Integer> resultKey = compareByKey(unsortMap); System.out.println(resultKey); System.out.println("Sort By Value..."); Map<String, Integer> resultValue = compareByValue(unsortMap); System.out.println(resultValue); } //Reference from java.util.Map source code, try dig inside, many generic examples. public static <K, V extends Comparable<? super V>> Map<K, V> compareByValue(Map<K, V> map) {  Map<K, V> result = new LinkedHashMap<>(); Stream<Map.Entry<K, V>> mapInStream = map.entrySet().stream(); mapInStream.sorted(Map.Entry.comparingByValue()) .forEachOrdered(x -> result.put(x.getKey(), x.getValue())); return result; } public static <K extends Comparable<? super K>, V> Map<K, V> compareByKey(Map<K, V> map) {  Map<K, V> result = new LinkedHashMap<>(); Stream<Map.Entry<K, V>> mapInStream = map.entrySet().stream(); mapInStream.sorted(Map.Entry.comparingByKey()) .forEachOrdered(x -> result.put(x.getKey(), x.getValue())); return result; } }

Output

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

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

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

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