Java Collection, HashMap Exercises: Test if a map contains a mapping for the specified key

Java Collection, HashMap Exercises: Exercise-7 with Solution

Write a Java program to test if a map contains a mapping for the specified key.

Sample Solution:-

Java Code:

import java.util.*;  
public class Example7 {  
   public static void main(String args[]) {
  HashMap < String, Integer > hash_map = new HashMap < String, Integer > ();
  hash_map.put("Red", 1);
  hash_map.put("Green", 2);
  hash_map.put("Black", 3);
  hash_map.put("White", 4);
  hash_map.put("Blue", 5);
  // print the map
  System.out.println("The Original map: " + hash_map);
  System.out.println("1. Is key 'Green' exists?");
  if (hash_map.containsKey("Green")) {
   //key exists
   System.out.println("yes! - " + hash_map.get("Green"));
  } else {
   //key does not exists

  System.out.println("\n2. Is key 'orange' exists?");
  if (hash_map.containsKey("orange")) {
   System.out.println("yes! - " + hash_map.get("orange"));
  } else {

Sample Output:

The Original map: {Red=1, White=4, Blue=5, Black=3, Green=2}           
1. Is key 'Green' exists?                                              
yes! - 2                                                               
2. Is key 'orange' exists?                                             

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