java 番石榴中是否有相应的不可变 enumMap ？
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Is there a corresponding immutable enumMap in guava?
提问by brainydexter
I recently learnt about the benefits of EnumMap in Java and would like to replace the existing ImmutableMap<OccupancyType, BigDecimal>to EnumMap. However, I'd also like the immutable property offered by ImmutableMap.
我最近了解了 Java 中 EnumMap 的好处，并想将现有的替换ImmutableMap<OccupancyType, BigDecimal>为 EnumMap。但是，我也喜欢 ImmutableMap 提供的不可变属性。
- Is there a variant, ImmutableEnumMap available in guava ?
- In terms of storage which one (EnumMap vs ImmutableMap) performs better ?
- I couldn't find a comparison of the two. I'd appreciate if someone can point me to a link or give some insights on the efficiency of the two data structures ?
- 番石榴中是否有变体 ImmutableEnumMap 可用？
- 在存储方面哪一个（EnumMap vs ImmutableMap）表现更好？
- 我找不到两者的比较。如果有人可以指出我的链接或对两种数据结构的效率提供一些见解，我将不胜感激？
回答by Louis Wasserman
Guava contributor here.
番石榴贡献者在这里。
Guava doesn't currently have an ImmutableEnumMapvariant, but if it did, it would probably just be a wrapper around an EnumMap. (That said, slightly better immutable implementations are possible.)
Guava 目前没有ImmutableEnumMap变体，但如果有，它可能只是一个EnumMap. （也就是说，稍微好一点的不可变实现是可能的。）
EnumMapwill perform better than the basic ImmutableMap, in any event; it's difficult or impossible to beat.
EnumMapImmutableMap无论如何都会比基本的表现更好；很难或不可能被击败。
(I'll file an issueto investigate adding an ImmutableMapvariant for enum key types, though.)
（不过，我将提交一个问题来调查ImmutableMap为枚举键类型添加变体。）
Update: Guava 14 adds Maps.immutableEnumMap().
更新：番石榴 14 添加了Maps.immutableEnumMap().
回答by The Alchemist
I was just wanted to provide an example now that ImmutableEnumMapis in Guava 14.0, because it's a package-private class, so you can't do ImmutableEnumMap.of(). You have to do Maps.immutableEnumMap()instead.
我只是想提供一个现在ImmutableEnumMap在Guava 14.0 中的例子，因为它是一个包私有类，所以你不能做ImmutableEnumMap.of(). 你必须这样做Maps.immutableEnumMap()。
private final ImmutableMap<MyEnum, String> myEnumMap = Maps.immutableEnumMap(ImmutableMap.of(
MyEnum.A, "A",
MyEnum.B, "B",
MyEnum.C, "C"
));
Not sure if there's a more natural syntax.
不确定是否有更自然的语法。
回答by jmh
As the guava ImmutableEnumMap is still marked beta as of version 14, I would suggest using a unmodifiable view of a enum map and then throwing away the original reference to the enum map to ensure that it is immutable.
由于 guava ImmutableEnumMap 在版本 14 中仍被标记为 beta，我建议使用枚举映射的不可修改视图，然后丢弃对枚举映射的原始引用以确保它是不可变的。
Example (in a constructor):
示例（在构造函数中）：
Map entries = new EnumMap <SomeEnum, T>(SomeEnum.class);
... // (fill in entries)
this.entries = Collections.unmodifiableMap(entries);
