List和set集合：交集、差集、合集的区别

set 、list集合的交集（retainAll）、差集(removeAll)是没有区别的都是一样的.

set 、list集合的合集addAll是有区别的：set可以去重复；list不去重复

public static void main(String[] args) {
            Set result = new HashSet();
            Set set1 = new HashSet(){{
                add(1);
                add(3);
                add(5);
            }};

            Set set2 = new HashSet(){{
                add(1);
                add(2);
                add(3);
            }};

            result.clear();
            result.addAll(set1);
            System.out.println("去重复交集前1："+set1);
            System.out.println("去重复交集前2："+set2);
            result.retainAll(set2);
            System.out.println("set1与set2的交集是："+result);

            result.clear();
            result.addAll(set2);
            System.out.println("差集前的1："+set1);
            System.out.println("差集前的2："+set2);
            result.removeAll(set1);
            System.out.println("set2与set1的差集是："+result);

            result.clear();
            result.addAll(set1);
            result.addAll(set2);
           
            System.out.print("set1和set2的并集："+result);
            System.err.print("set1集合并集：是去重复"+"\n");
            
            
            
            List list = new ArrayList();
            List list1 = new ArrayList(){{
                add(1);
                add(3);
                add(5);
            }};

            List list2 = new ArrayList(){
            {
                add(1);
                add(2);
                add(3);
            }};

            list.clear();
            list.addAll(list1);
            System.out.println("去重复交集前1："+list1);
            System.out.println("去重复交集前2："+list2);
            list.retainAll(list2);
            System.out.println("list1与list2的交集是："+list);

            list.clear();
            list.addAll(list2);
            System.out.println("差集前的1："+list1);
            System.out.println("差集前的2："+list2);
            list.removeAll(list1);
            System.out.println("list2与list1的差集是："+list);

            list.clear();
            list.addAll(list1);
            list.addAll(list2);
            
            System.out.print("list1和set2的并集："+list);
            System.err.print("List集合并集：是不会去重复");

        }

输出结果：

去重复交集前1：[1, 3, 5]
去重复交集前2：[1, 2, 3]
set1与set2的交集是：[1, 3]
差集前的1：[1, 3, 5]
差集前的2：[1, 2, 3]
set2与set1的差集是：[2]
set1和set2的并集：[1, 2, 3, 5]set1集合并集：是去重复 

去重复交集前1：[1, 3, 5]
去重复交集前2：[1, 2, 3]
list1与list2的交集是：[1, 3]
差集前的1：[1, 3, 5]
差集前的2：[1, 2, 3]
list2与list1的差集是：[2]
list1和set2的并集：[1, 3, 5, 1, 2, 3]List集合并集：是不会去重复