Here you can find the source of addAll(Collection
public static <E> boolean addAll(Collection<E> addTo, Iterable<? extends E> elementsToAdd)
//package com.java2s; /*/*from w w w. j a v a2 s . c om*/ * Copyright (C) 2009 The Guava Authors * * Licensed 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.*; public class Main { public static <E> boolean addAll(Collection<E> addTo, Iterable<? extends E> elementsToAdd) { boolean modified = false; for (E e : elementsToAdd) { modified |= addTo.add(e); } return modified; } }