set取交集、并集、差集

HashSet<String> hashSet = new HashSet<>(Arrays.asList("0", "1", "2"));
HashSet<String> hashSet2 = new HashSet<>(Arrays.asList("1", "2", "3"));
// 取交集
hashSet.retainAll(hashSet2);
hashSet.forEach(System.out::println);
System.out.println();
HashSet<String> hashSet3 = new HashSet<>(Arrays.asList("0", "1", "2"));
// 取并集
hashSet3.addAll(hashSet2);
hashSet3.forEach(System.out::println);
System.out.println();
HashSet<String> hashSet4 = new HashSet<>(Arrays.asList("0", "1", "2"));
// 取差集
hashSet4.removeAll(hashSet2);
hashSet4.forEach(System.out::println);