Java Collection, TreeMap Exercises: Sort keys in Tree Map by using comparator

Java Collection, TreeMap Exercises: Exercise-7 with Solution

Write a Java program to sort keys in Tree Map by using comparator.

Sample Solution:-

Java Code:

import java.util.*;
import java.util.Map.Entry;  
public class Example7 {  
    public static void main(String args[]){  
  TreeMap<String,String> tree_map1 = new TreeMap<String,String>(new sort_key());
   // Put elements to the map 
  tree_map1.put("C2", "Red");
  tree_map1.put("C4", "Green");
  tree_map1.put("C3", "Black");
  tree_map1.put("C1", "White"); 
 class sort_key implements Comparator<String>{
    public int compare(String str1, String str2) {
        return str1.compareTo(str2);

Sample Output:

{C1=White, C2=Red, C3=Black, C4=Green} 

Java Code Editor:

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Java: Tips of the Day


Converts to enum to Map where key is the name and value is Enum itself.

public static <E extends Enum<E>> Map<String, E> getEnumMap(final Class<E> enumClass) {
    return Arrays.stream(enumClass.getEnumConstants())
            .collect(Collectors.toMap(Enum::name, Function.identity()));

Ref: https://bit.ly/3xXcFZt