Here you can find the source of sort(List> list1, List> list2)
public static int sort(List<?> list1, List<?> list2)
//package com.java2s; //License from project: Open Source License import java.util.List; public class Main { public static int sort(List<?> list1, List<?> list2) { return list2.size() - list1.size(); }// ww w. j a va 2s .c om }