EnumMap class in Java

The java.util.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.

Following are the constructors of the EnumMap class −

Example

Let us see an example −

 Live Demo

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 us see another example wherein we are displaying the count of key-value mappings in the Map −

 Live Demo

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