Java Collection, TreeMap Exercises: Get the first (lowest) key and the last (highest) key currently in a map

Java Collection, TreeMap Exercises: Exercise-9 with Solution

Write a Java program to get the first (lowest) key and the last (highest) key currently in a map.

Sample Solution:-

Java Code:

import java.util.*;
import java.util.Map.Entry;  
public class Example9 {  
     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("Greatest key: " + tree_map1.firstKey());
  System.out.println("Least key: " + tree_map1.lastKey());

Sample Output:

Orginal TreeMap content: {C1=Green, C2=Red, C3=White, C4=Black}        
Greatest key: C1                                                       
Least key: C4

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