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Showing content from https://www.tutorialspoint.com/java/util/java_util_enummap.htm below:

Java EnumMap Class

Java EnumMap Class Introduction

The Java EnumMap class is a specialized Map implementation for use with enum keys.Following are the important points about EnumMap −

All of the keys in an enum map must come from a single enum type that is specified, explicitly or implicitly, when the map is created.
Enum maps are maintained in the natural order of their keys.
EnumMap is not synchronized.If multiple threads access an enum map concurrently, and at least one of the threads modifies the map, it should be synchronized externally.

Class declaration

Following is the declaration for java.util.EnumMap class −

public class EnumMap<K extends Enum<K>,V>
   extends AbstractMap<K,V>
   implements Serializable, Cloneable

Class constructors Sr.No. Constructor & Description 1

EnumMap(Class<K> keyType)

This constructor creates an empty enum map with the specified key type.

EnumMap(EnumMap<K,? extends V> m)

This constructor creates an enum map with the same key type as the specified enum map, initially containing the same mappings (if any).

EnumMap(Map<K,? extends V> m)

This constructor creates an enum map initialized from the specified map.

Class methods Methods inherited

This class inherits methods from the following classes −

java.util.AbstractMap
java.util.Object

Adding a Key-Value to an EnumMap Of Enum, Integer Pair Example

The following example shows the usage of Java EnumMap put(K,V) method to put a value in the EnumMap instance. We've created a enum Numbers. Then EnumMap is created of enum Numbers and Integer. Few entries are added using put(K,V) and enumMap is printed. Using put() method again, a value of enumMap is replaced and map is printed again.

package com.tutorialspoint;

import java.util.EnumMap;

public class EnumMapDemo {
   
   // create an enum
   public enum Numbers{ONE, TWO, THREE, FOUR, FIVE}; 

   public static void main(String[] args) {
      
      EnumMap<Numbers,Integer> map = 
         new EnumMap<>(Numbers.class);

      // associate values in map
      map.put(Numbers.ONE, 1);
      map.put(Numbers.TWO, 2);
      map.put(Numbers.THREE,3);

      // print the whole map
      System.out.println(map); 

      map.put(Numbers.THREE, 4);
	  
      // print the updated map
      System.out.println(map);
   }
}

Let us compile and run the above program, this will produce the following result −

{ONE=1, TWO=2, THREE=3}
{ONE=1, TWO=2, THREE=4}

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