示例

package com.example;import java.util.ArrayList;import java.util.Arrays;import java.util.Collections;import java.util.List;public class ListOpt {    private List intersect(List ls1, List ls2) {        List list = new ArrayList(Arrays.asList(new Object[ls1.size()]));        Collections.copy(list, ls1);        list.retainAll(ls2);        return list;    }    private List union(List ls1, List ls2) {        List list = new ArrayList(Arrays.asList(new Object[ls1.size()]));        Collections.copy(list, ls1);        list.addAll(ls2);        return list;    }    private List diff(List ls1, List ls2) {        List list = new ArrayList(Arrays.asList(new Object[ls1.size()]));        Collections.copy(list, ls1);        list.removeAll(ls2);        return list;    }    public static void main(String[] args) {        List
     
       l1 = new ArrayList
      
       () {
    {            add(1);            add(2);            add(3);        }};        List
       
         l2 = new ArrayList
        
         () {
    {            add(2);            add(3);            add(4);        }};        ListOpt opt = new ListOpt();        List intersectList = opt.intersect(l1, l2);        List union = opt.union(l1, l2);        List diff = opt.diff(l1, l2);        print(intersectList);        print(union);        print(diff);    }    private static void print(List lst) {        if (lst.size() == 0) {            return;        }        for (int i = 0; i 
        
       
      
     

输出

23---123234---1---

注

在操作之前对原对象进行了拷贝，如果对原对象直接操作会修改原来的对象

另一种写法

/** * Created by yuhui on 2017/7/11 0011. */import java.util.HashSet;import java.util.Set;public class TestSet {    public static void main(String[] args) {        Set
     
       result = new HashSet
      
       ();        Set
       
         set1 = new HashSet
        
         () {            {                add("王者荣耀");                add("英雄联盟");                add("穿越火线");                add("地下城与勇士");            }           };        Set
         
           set2 = new HashSet
          
           () { { add("王者荣耀"); add("地下城与勇士"); add("魔兽世界"); } }; result.clear(); result.addAll(set1); result.retainAll(set2); System.out.println("交集：" + result); result.clear(); result.addAll(set1); result.removeAll(set2); System.out.println("差集：" + result); result.clear(); result.addAll(set1); result.addAll(set2); System.out.println("并集：" + result); }}