Here you can find the source of subtract(Collection
public static <T> ArrayList<T> subtract(Collection<T> l1, Collection<T> l2)
//package com.java2s; //License from project: Open Source License import java.util.ArrayList; import java.util.Collection; public class Main { public static <T> ArrayList<T> subtract(Collection<T> l1, Collection<T> l2) { ArrayList<T> al = new ArrayList<T>(); al.addAll(l1);// ww w .j a v a 2 s .com for (T item : l2) { al.remove(item); } return al; } }