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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 ..

package com.bethecoder.java8.streams;

import java.util.Arrays;
import java.util.Comparator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public class SortMapExample {

public static void main(String[] args) {
		List<Student> sudents = Arrays.asList(
				new Student(1, "Sriram", 12),
				new Student(2, "Tanvie", 6),
				new Student(3, "Charan", 10)
		);
		
		Map<String, Integer> studentMap = sudents.stream()
				.collect(Collectors.toMap(Student::getName, Student::getAge));
		System.out.println("Unordered: " + studentMap);
		
		
		//Sort by Key
		Map<String, Integer> sortedByName = studentMap.entrySet().stream()
				.sorted(Map.Entry.comparingByKey(Comparator.naturalOrder()))
				.collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, 
						(oldValue, newValue) -> oldValue, LinkedHashMap::new));
		
		System.out.println("Sort by Key: " + sortedByName);
		
		
		//Sort by Value
		Map<String, Integer> sortedByAge = studentMap.entrySet().stream()
				.sorted(Map.Entry.comparingByValue(Comparator.reverseOrder()))
				.collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, 
						(oldValue, newValue) -> oldValue, LinkedHashMap::new));
		
		System.out.println("Sort by Value: " + sortedByAge);
	}

private static class Student {
		private int id;
		private String name;
		private int age;

public Student(int id, String name, int age) {
			this.id = id;
			this.name = name;
			this.age = age;
		}

public int getId() {
			return id;
		}

public void setId(int id) {
			this.id = id;
		}

public String getName() {
			return name;
		}

public void setName(String name) {
			this.name = name;
		}

public int getAge() {
			return age;
		}

public void setAge(int age) {
			this.age = age;
		}

}
}

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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