EnumMap Class
In this chapter you will learn:
Use 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>
Kspecifies the type of keyVspecifies the type of value.Kmust 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;
/*ja va2s . com*/
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 code above generates the following result.
Map from enum to integer
The following code maps enum to an integer.
import java.util.EnumMap;
import java.util.Map;
/*from ja v a 2s . co m*/
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);
}
}
Next chapter...
What you will learn in the next chapter:
- What is PriorityQueue Class and how to use PriorityQueue Class
- Using a comparator with a priority queu