是否有更高效和专业的Map集合实现,其中Enum对象可以作为键?
Yes. EnumMap
is precisely that; an efficient implementation of the Map
interface, in which the key type must be an enum:
From the API documentation
:
Class EnumMap<K extends Enum<K>,V>
A specialized Map implementation for use with enum type keys. 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 represented internally as arrays. This representation is extremely compact and efficient.
Example usage:
Map<MyEnum, String> map = new EnumMap<MyEnum, String>(MyEnum.class);
BTW, it's simpler to write:
Map<MyEnum, String> map = new EnumMap<>(MyEnum.class);
There's no need to repeat the types. This can make the code a lot easier to read.
I learned this recently after I accidentally stumbled upon the answer in the Java API. If you ever have a map that uses enums as keys make sure you use EnumMap . It's very simple and much more efficient:
public interface LibraryItem{ ... }
public enum LibraryItemType{ BOOK, CD, VHS, AUDIO; ... }
Map<LibraryItemType, NavigableSet<LibraryItem>> itemsByType =
new EnumMap<>(LibraryItemType.class);
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