java 集合取交集

1.使用retainAll()方法：

List<Integer> list1 = new ArrayList<>(Arrays.asList(1, 2, 3));
List<Integer> list2 = new ArrayList<>(Arrays.asList(2, 3, 4));
list1.retainAll(list2);
System.out.println(list1); // 输出 [2, 3]

Set<Integer> set1 = new HashSet<>(Arrays.asList(1, 2, 3));
Set<Integer> set2 = new HashSet<>(Arrays.asList(2, 3, 4));
set1.retainAll(set2);
System.out.println(set1); // 输出 [2, 3]

2.使用Java 8的stream的filter方法和collect方法：

List<Integer> list1 = new ArrayList<>(Arrays.asList(1, 2, 3));
List<Integer> list2 = new ArrayList<>(Arrays.asList(2, 3, 4));
List<Integer> intersection = list1.stream().filter(e -> list2.contains(e)).collect(Collectors.toList());
System.out.println(intersection); // 输出 [2, 3]