Here you can find the source of diff(Collection
public static <T> Collection<T> diff(Collection<T> c1, Collection<T> c2)
//package com.java2s; /**//ww w . ja va 2 s . c o m * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF licenses this file * to you under the Apache License, Version 2.0 (the * "License"); you may not use this file except in compliance * with the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, * software distributed under the License is distributed on an * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY * KIND, either express or implied. See the License for the * specific language governing permissions and limitations * under the License. */ import java.util.ArrayList; import java.util.Collection; public class Main { public static <T> Collection<T> diff(Collection<T> c1, Collection<T> c2) { if (c1 == null || c1.size() == 0 || c2 == null || c2.size() == 0) { return c1; } Collection<T> difference = new ArrayList<T>(); for (T item : c1) { if (!c2.contains(item)) { difference.add(item); } } return difference; } }