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Java Collection, HashMap Exercises: Count the number of key-value (size) mappings in a map

Java Collection, HashMap Exercises: Exercise-2 with Solution

Write a Java program to count the number of key-value (size) mappings in a map.

Sample Solution:-

Java Code:

import java.util.*;  
public class Example2 {  
   public static void main(String args[]){  
  HashMap<Integer,String> hash_map= new HashMap<Integer,String>();  
  hash_map.put(1, "Red");
  hash_map.put(2, "Green");
  hash_map.put(3, "Black");
  hash_map.put(4, "White");
  hash_map.put(5, "Blue");
  System.out.println("Size of the hash map: "+hash_map.size());
 }
}

Sample Output:

Size of the hash map: 5 

Java Code Editor:

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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