交集和并集
public static void main(String[] args) {List<Integer> list1 = new ArrayList<>();List<Integer> list2 = new ArrayList<>();list1.add(1);list1.add(2);list1.add(3);list2.add(2);list2.add(3);list2.add(4);boolean b = list1.retainAll(list2);System.out.println(list1);if (b){System.out.println("888");}list1.removeAll(list2);list1.addAll(list2);System.out.println(list1);}