The EnumMap Class
EnumMap extends AbstractMap and implements Map. It uses an enum type as keys.
The EnumMap class provides a Map implementation whose keys are the members of the same enum. Null keys are not permitted.
It is a generic class that has this declaration:
class EnumMap<K extends Enum<K>, V>
- K specifies the type of key
- V specifies the type of value.
- K must extend Enum<K>, which enforces that hat the keys must be of an enum type.
EnumMap defines the following constructors:
EnumMap(Class<K> kType)- creates an empty EnumMap of type kType.
EnumMap(Map<K, ? extends V> m)- creates an EnumMap map that contains the same entries as m.
EnumMap(EnumMap<K, ? extends V> em)- creates an EnumMap initialized with the values in em.
The following code stores Size enum to a EnumMap.
import java.util.EnumMap;
public class Main {
public static void main(String[] args) {
EnumMap<Size, String> sizeMap = new EnumMap<Size, String>(Size.class);
sizeMap.put(Size.S, "S");
sizeMap.put(Size.M, "M");
sizeMap.put(Size.L, "L");
sizeMap.put(Size.XL, "XL");
sizeMap.put(Size.XXL, "XXL");
sizeMap.put(Size.XXXL, "XXXL");
for (Size size : Size.values()) {
System.out.println(size + ":" + sizeMap.get(size));
}
}
}
enum Size {
S, M, L, XL, XXL, XXXL;
}
The following code maps enum to an integer.
import java.util.EnumMap;
import java.util.Map;
enum Coin {
PENNY, NICKEL, DIME, QUARTER
}
public class Main {
public static void main(String[] args) {
Map<Coin, Integer> map = new EnumMap<Coin, Integer>(Coin.class);
map.put(Coin.PENNY, 1);
map.put(Coin.NICKEL, 5);
map.put(Coin.DIME, 10);
map.put(Coin.QUARTER, 25);
System.out.println(map);
Map<Coin, Integer> mapCopy = new EnumMap<Coin, Integer>(map);
System.out.println(mapCopy);
}
}