EnumMap class in Java

The java.util.EnumMap class is a Map implementation specifically used to enumerate keys. Here are the important points about EnumMap:

• All keys in an enum map must come from a specified enum type, either explicitly or implicitly when creating the map.

• Enumeration mappings are maintained in the natural order of keys.

• EnumMap is not synchronized. If multiple threads access an enumeration map simultaneously, and at least one thread modifies the map, synchronization should be done externally.

The following is the constructor of the EnumMap class:

##123 table>Example

Let’s see an example-

Live Demonstration

import java.util.EnumMap;
public class Demo {
   // create an enum
   public enum Numbers {
      ONE, TWO, THREE, FOUR, FIVE
   };
   public static void main(String[] args) {
      EnumMap<Numbers, String> map1 = new EnumMap<Numbers, String>(Numbers.class);
      EnumMap<Numbers, String> map2 = new EnumMap<Numbers, String>(Numbers.class);
      // associate values in map1
      map1.put(Numbers.ONE, "1");
      map1.put(Numbers.TWO, "2");
      map1.put(Numbers.THREE, "3");
      map1.put(Numbers.FOUR, "4");
      // print the whole map
      System.out.println("map1:" + map1);
      // clone map1 to map2
      map2 = map1.clone();
      // print map2
      System.out.println("map2:" + map2);
   }
}

Output

map1:{ONE=1, TWO=2, THREE=3, FOUR=4}
map2:{ONE=1, TWO=2, THREE=3, FOUR=4}

Example

Let’s look at another example where we show the count of key-value mappings in a Map:

Live Demonstration

import java.util.*;
public class EnumMapDemo {
   // create an enum
   public enum Numbers {
      ONE, TWO, THREE, FOUR, FIVE
   };
   public static void main(String[] args) {
      EnumMap<Numbers, String> map = new EnumMap<Numbers, String>(Numbers.class);
      // assosiate values in map
      map.put(Numbers.ONE, "1");
      map.put(Numbers.TWO, "2");
      map.put(Numbers.THREE, "3");
      map.put(Numbers.FOUR, "4");
      // print the map
      System.out.println("Map: " + map);
      // print the number of mappings of this map
      System.out.println("Number of mappings:" + map.size());
      // remove value from Numbers.THREE
      map.put(Numbers.FIVE, "5");
      // print the new number of mappings of this map
      System.out.println("Number of mappings:" + map.size());
   }
}

Output

Map: {ONE=1, TWO=2, THREE=3, FOUR=4}
Number of mappings:4
Number of mappings:5

Serial number	Constructor and description
	EnumMap(Class keyType)This constructor is created using the specified key type An empty enum map.
	EnumMap(EnumMap m)The The constructor creates an enum map using the same key types as the specified enum map, Initially contains the same mapping if available.
	EnumMap(Map m)This The constructor creates an enum map initialized from the specified map.

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