如何使用Java 8流API存储枚举 [英] How to store enum to map using Java 8 stream API

问题描述

我有一个枚举与另一个枚举作为参数

I have an enum with another enum as a parameter

public enum MyEntity{
   Entity1(EntityType.type1,
    ....


   MyEntity(EntityType type){
     this.entityType = entityType;
   }
}

我想创建一个方法，返回枚举按类型

I want to create a method that return the enum by type

public MyEntity getEntityTypeInfo(EntityType entityType) {
        return lookup.get(entityType);
    }

通常我会写

private static final Map<EntityType, EntityTypeInfo> lookup = new HashMap<>();

static {
    for (MyEntity d : MyEntity.values()){
        lookup.put(d.getEntityType(), d);
    }
}

用java流写最好的做法是什么？ >

What is the best practice to write it with java stream?

推荐答案

我想有一些你的代码中的打字错误（该方法在我看来应该是静态的，你的构造函数目前正在做一个no-op），但是如果我跟着你，你可以从枚举数组中创建一个流，然后使用 toMap collector，将每个枚举与它的 EntityType 映射到键，并将实例本身映射为一个值：

I guess there are some typos in your code (the method should be static in my opinion, your constructor is doing a no-op at the moment), but if I'm following you, you can create a stream from the array of enums and use the toMap collector, mapping each enum with its EntityType for the keys, and mapping the instance itself as a value:

private static final Map<EntityType, EntityTypeInfo> lookup =
    Arrays.stream(EntityTypeInfo.values())
          .collect(Collectors.toMap(EntityTypeInfo::getEntityType, e -> e));

toMap 收藏者的不保证关于返回的地图实现（尽管它目前是一个 HashMap ），但您可以随时使用 overloaded variant如果需要更多的控件，提供一个投掷合并作为参数。

The toMap collector does not make any guarantee about the map implementation returned (although it's currently a HashMap), but you can always use the overloaded variant if you need more control, providing a throwing merger as parameter.

你也可以使用静态类的另一个技巧，并将地图填写在构造函数。

You could also use another trick with a static class, and fill the map in the constructor.

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