ListUtil(差集、交集、并集)

 package cn.fraudmetrix.octopus.horai.biz.utils;

 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;

 /**
  * Created by hunt on 2017/7/31.
  */
 @SuppressWarnings("all")
 public class ListUtil {
     /**
      * 求ls对ls2的差集,即ls中有，但ls2中没有的
      *
      * @param ls
      * @param ls2
      * @return
      */
     public static List diff(List ls, List ls2) {
         List list = new ArrayList(Arrays.asList(new Object[ls.size()]));
         Collections.copy(list, ls);
         list.removeAll(ls2);
         return list;
     }

     /**
      * 求2个集合的交集
      *
      * @param ls
      * @param ls2
      * @return
      */
     public static List intersect(List ls, List ls2) {
         List list = new ArrayList(Arrays.asList(new Object[ls.size()]));
         Collections.copy(list, ls);
         list.retainAll(ls2);
         return list;
     }

     /**
      * 求2个集合的并集
      *
      * @param ls
      * @param ls2
      * @return
      */
     public static List union(List ls, List ls2) {
         List list = new ArrayList(Arrays.asList(new Object[ls.size()]));
         Collections.copy(list, ls);//将ls的值拷贝一份到list中
         list.removeAll(ls2);
         list.addAll(ls2);
         return list;
     }
 }