w3resource

Java Collection, TreeMap Exercises: Get a reverse order view of the keys contained in a given map

Java Collection, TreeMap Exercises: Exercise-10 with Solution

Write a Java program to get a reverse order view of the keys contained in a given map.

Sample Solution:-

Java Code:

import java.util.*;
import java.util.Map.Entry;  
public class Example10 {  
     public static void main(String args[]) {

  // Create a tree map
  TreeMap <String,String> tree_map1 = new TreeMap <String,String> ();

  // Put elements to the map 
  tree_map1.put("C2", "Red");
  tree_map1.put("C1", "Green");
  tree_map1.put("C4", "Black");
  tree_map1.put("C3", "White");

  System.out.println("Orginal TreeMap content: " + tree_map1);
  System.out.println("Reverse order view of the keys: " + tree_map1.descendingKeySet());
 }
}

Sample Output:

Orginal TreeMap content: {C1=Green, C2=Red, C3=White, C4=Black}        
Reverse order view of the keys: [C4, C3, C2, C1]

Java Code Editor:

Contribute your code and comments through Disqus.

Previous: Get the first (lowest) key and the last (highest) key currently in a map.
Next: Get a key-value mapping associated with the greatest key less than or equal to the given key.

What is the difficulty level of this exercise?

Test your Programming skills with w3resource's quiz.



Share this Tutorial / Exercise on : Facebook and Twitter

Java: Tips of the Day

getEnumMap

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