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 Java 8 Features > Stream API > Sort Map by Key and Value

Sort Map by Key and Value

Author: Venkata Sudhakar

The below example shows how to ..

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01package com.bethecoder.java8.streams;
02 
03import java.util.Arrays;
04import java.util.Comparator;
05import java.util.LinkedHashMap;
06import java.util.List;
07import java.util.Map;
08import java.util.stream.Collectors;
09 
10public class SortMapExample {
11 
12    public static void main(String[] args) {
13        List<Student> sudents = Arrays.asList(
14                new Student(1, "Sriram", 12),
15                new Student(2, "Tanvie", 6),
16                new Student(3, "Charan", 10)
17        );
18         
19        Map<String, Integer> studentMap = sudents.stream()
20                .collect(Collectors.toMap(Student::getName, Student::getAge));
21        System.out.println("Unordered: " + studentMap);
22         
23         
24        //Sort by Key
25        Map<String, Integer> sortedByName = studentMap.entrySet().stream()
26                .sorted(Map.Entry.comparingByKey(Comparator.naturalOrder()))
27                .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue,
28                        (oldValue, newValue) -> oldValue, LinkedHashMap::new));
29         
30        System.out.println("Sort by Key: " + sortedByName);
31         
32         
33        //Sort by Value
34        Map<String, Integer> sortedByAge = studentMap.entrySet().stream()
35                .sorted(Map.Entry.comparingByValue(Comparator.reverseOrder()))
36                .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue,
37                        (oldValue, newValue) -> oldValue, LinkedHashMap::new));
38         
39        System.out.println("Sort by Value: " + sortedByAge);
40    }
41 
42    private static class Student {
43        private int id;
44        private String name;
45        private int age;
46 
47        public Student(int id, String name, int age) {
48            this.id = id;
49            this.name = name;
50            this.age = age;
51        }
52 
53        public int getId() {
54            return id;
55        }
56 
57        public void setId(int id) {
58            this.id = id;
59        }
60 
61        public String getName() {
62            return name;
63        }
64 
65        public void setName(String name) {
66            this.name = name;
67        }
68 
69        public int getAge() {
70            return age;
71        }
72 
73        public void setAge(int age) {
74            this.age = age;
75        }
76 
77    }
78}

It gives the following output, 

Unordered: {Tanvie=6, Sriram=12, Charan=10}
Sort by Key: {Charan=10, Sriram=12, Tanvie=6}
Sort by Value: {Sriram=12, Charan=10, Tanvie=6}

 
  


  
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