如何使用 Java 8 流 API 存储枚举以进行映射
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How to store enum to map using Java 8 stream API
提问by Bick
I have an enumwith another enumas a parameter
我有一个enum与另一个enum作为参数
public enum MyEntity{
Entity1(EntityType.type1,
....
MyEntity(EntityType type){
this.entityType = entityType;
}
}
I want to create a method that return the enumby type
我想创建一个返回enumby 类型的方法
public MyEntity getEntityTypeInfo(EntityType entityType) {
return lookup.get(entityType);
}
usually I would have written
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);
}
}
What is the best practice to write it with java stream?
用java流编写它的最佳实践是什么？
回答by Alexis C.
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 toMapcollector, mapping each enum with its EntityTypefor the keys, and mapping the instance itself as a value:
我猜您的代码中有一些拼写错误（我认为该方法应该是静态的，您的构造函数目前正在执行无操作），但是如果我关注您，您可以从枚举数组中创建一个流并使用toMap收集器，将每个枚举与其EntityType键映射，并将实例本身映射为值：
private static final Map<EntityType, EntityTypeInfo> lookup =
Arrays.stream(EntityTypeInfo.values())
.collect(Collectors.toMap(EntityTypeInfo::getEntityType, e -> e));
The toMapcollector does not make any guarantee about the map implementation returned (although it's currently a HashMap), but you can always use the overloadedvariant if you need more control, providing a throwing merger as parameter.
该toMap回收不作出关于返回的映射实现任何保证（尽管它目前是HashMap），但你总是可以使用重载的变种，如果你需要更多的控制，提供了一个投掷合并为参数。
You could also use another trick with a static class, and fill the map in the constructor.
回答by dobrivoje
public enum FibreSpeed {
a30M( "30Mb Fibre Connection - Broadband Only", 100 ),
a150M( "150Mb Fibre Connection - Broadband Only", 300 ),
a1G( "1Gb Fibre Connection - Broadband Only", 500 ),
b30M( "30Mb Fibre Connection - Broadband & Phone", 700 ),
b150M( "150Mb Fibre Connection - Broadband & Phone", 900 ),
b1G( "1Gb Fibre Connection - Broadband & Phone", 1000 );
public String speed;
public int weight;
FibreSpeed(String speed, int weight) {
this.speed = speed;
this.weight = weight;
}
public static Map<String, Integer> SPEEDS = Stream.of( values() ).collect( Collectors.toMap( k -> k.speed, v -> v.weight ) );
}
