英文:
Java streams compare object from two streams and create new Object
问题
我有两个列表：
List<Object1> listOne = provider.getObjects().stream().collect(Collectors.toList());
List<Object2> listTwo = provider2.getObjects().stream().collect(Collectors.toList());
现在我想创建一个包含所有可能的 Object1-Object2 组合的列表：List<ObjectCombinations> result;
class ObjectCombinations {
Object1 object1;
Object2 object2;
public ObjectCombinations(Object1 object1, Object2 object2) {
this.object1 = object1;
this.object2 = object2;
}
}
如何在 Java 8 的流中实现这个功能？
英文:
I have two Lists:
List<Object1> listOne = provider.getObjects().stream().collect(Collectors.toList());
List<Object2> listTwo = provider2.getObjects().stream().collect(Collectors.toList());
Now I want create List containg all possible Object1-Object2 combinations: List<ObjectCombinations> result;
class ObjectCombinations {
Object1 object1;
Object2 object2;
public ObjectCombinations(Object1 object1, Object2 object2) {
this.object1 = object1;
this.object2 = object2;
}
}
How is that possible with java 8 streams?
答案1
得分: 2
你可以使用 flatMap 来获取所有的组合：
List<ObjectCombinations> result =
listOne.stream()
.flatMap(o1 -> listTwo.stream()
.map(o2 -> new ObjectCombinations(o1,o2)))
.collect(Collectors.toList());
首先，你创建一个 Stream<Object1>，然后使用 flatMap 将该流的每个元素与 listTwo 的所有元素组合，并创建 ObjectCombinations 实例，然后将其收集到一个 List 中。
英文:
You can use flatMap to get all the combinations:
List<ObjectCombinations> result =
listOne.stream()
.flatMap(o1 -> listTwo.stream()
.map(o2 -> new ObjectCombinations(o1,o2)))
.collect(Collectors.toList());
First you create a Stream<Object1>, then you use flatMap to combine each element of that stream with all the elements of listTwo, and create the ObjectCombinations instances, which you collect to a List.
答案2
得分: 1
你可以在需要遍历第二个列表并创建ObjectCombinations并扁平化列表的地方使用flatMap。
List<ObjectCombinations> res =
listOne.stream()
.flatMap(a -> listTwo.stream().map(b -> new ObjectCombinations(a, b)))
.collect(Collectors.toList());
英文:
You can use flatMap where you can stream over 2nd list and create ObjectCombinations and flatten the list.
List<ObjectCombinations> res =
listOne.stream()
.flatMap(a -> listTwo.stream().map(b -> new ObjectCombinations(a,b)))
.collect(Collectors.toList());
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