哪位大神帮我看下这JAVA代码有什么问题？为什么后面的结果不正确？

import java.util.*; public class Main { public static void main(String[] args) { ArrayList<String> a=new ArrayList<>(); ArrayList<String> b=new ArrayList<>(); ArrayList<String> c=new ArrayList<>(); a.add("1,2,3,4,5,6,7"); a.add("1,3,9,4,5,6,8"); a.add("4,3,4,5,6,7,8"); a.add("1,2,3,4,7,8,9"); a.add("1,7,3,5,7,8,10"); a.add("1,2,3,4,6,7,8"); a.add("1,2,3,4,5,6,7"); a.add("11,12,13,14,15,16,17"); b.add("1,2"); b.add("5,6"); for (String s1 : b) { int cnt=0; List list1 = new ArrayList<String>(Arrays.asList(s1.split(","))); for (String s2 : a) { List list2 = new ArrayList<String>(Arrays.asList(s2.split(","))); list1.retainAll(list2); if(list1==null){ cnt++; } else{ cnt=0; } System.out.println(list1); System.out.println(list2); System.out.println(cnt); }} } }