在Java中合并多个列表 [英] Combine multiple lists in Java

问题描述

如果要用Java将两个列表合并为一个列表，可以使用ListUtils.union(List list1,List list2).但是，如果我想合并多个列表怎么办?

If I want to make two lists into one in Java, I can use ListUtils.union(List list1,List list2). But what if I want to combine multiple lists?

这有效:

import org.apache.commons.collections.ListUtils;
List<Integer>list1=Arrays.asList(1,2,3);
List<Integer>list2=Arrays.asList(4,5,6);
List<Integer>list3=Arrays.asList(7,8,9);
List<Integer>list4=Arrays.asList(10,0,-1);
System.out.println(ListUtils.union(ListUtils.union(list1, list2),ListUtils.union(list3, list4)));

但是，它看起来并不是真正的最佳解决方案，阅读起来也不是特别好.可悲的是ListUtils.union(list1,list2,list3,list4)不起作用.多次使用addAll并为所有条目重复创建自己的列表对我来说似乎也不理想.那我该怎么办呢?

But it doesn't really look like the best solution, neither is it particularly great to read. Sadly ListUtils.union(list1,list2,list3,list4) doesn't work. Using addAll multiple times and creating its own list just for that with duplicates of all the entries also doesn't seem ideal to me. So what can I do instead?

推荐答案

Java 8借助

Java 8 has an easy way of doing it with the help of Stream API shown in the code below. We have basically created a stream with all the lists , and then as we need the individual contents of the lists, there is a need to flatten it with flatMap and finally collect the elements in a List.

List<Integer>list1=Arrays.asList(1,2,3);
List<Integer>list2=Arrays.asList(4,5,6);
List<Integer>list3=Arrays.asList(7,8,9);
List<Integer>list4=Arrays.asList(10,0,-1);
List<Integer> newList = Stream.of(list1, list2, list3,list4)
                                      .flatMap(Collection::stream)
                                      .collect(Collectors.toList());       
 System.out.println(newList); // prints [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 0, -1]

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