Here you can find the source of addAll(Collection
public static <E> boolean addAll(Collection<E> c, Iterable<? extends E> elts)
//package com.java2s; /*BEGIN_COPYRIGHT_BLOCK* /*from w ww.j a v a 2 s. com*/ PLT Utilities BSD License Copyright (c) 2007-2010 JavaPLT group at Rice University All rights reserved. Developed by: Java Programming Languages Team Rice University http://www.cs.rice.edu/~javaplt/ Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: - Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. - Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. - Neither the name of the JavaPLT group, Rice University, nor the names of the library's contributors may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS AND CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. *END_COPYRIGHT_BLOCK*/ import java.util.*; public class Main { /** * Add the given elements to a collection. Unlike {@link Collection#addAll}, defined for arbitrary * {@code Iterable}s. When possible, delegates to {@code c.addAll()}. * @return {@code true} if {@code c} changed as a result of the call */ public static <E> boolean addAll(Collection<E> c, Iterable<? extends E> elts) { if (elts instanceof Collection<?>) { @SuppressWarnings("unchecked") // should be legal, but javac 6 doesn't like it Collection<? extends E> eltsColl = (Collection<? extends E>) elts; return c.addAll(eltsColl); } else { boolean result = false; for (E elt : elts) { result |= c.add(elt); } return result; } } }