1 /* 2 * Copyright (c) 2002, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 */ 23 24 /* 25 * @test 26 * @bug 4684279 27 * @summary Empty utility collections should be singletons 28 * @author Josh Bloch 29 */ 30 31 import java.util.*; 32 import java.io.*; 33 34 public class EmptyCollectionSerialization { 35 private static Object patheticDeepCopy(Object o) throws Exception { 36 // Serialize 37 ByteArrayOutputStream bos = new ByteArrayOutputStream(); 38 ObjectOutputStream oos = new ObjectOutputStream(bos); 39 oos.writeObject(o); 40 byte[] serializedForm = bos.toByteArray(); 41 42 // Deserialize 43 InputStream is = new ByteArrayInputStream(serializedForm); 44 ObjectInputStream ois = new ObjectInputStream(is); 45 return ois.readObject(); 46 } 47 48 private static boolean isSingleton(Object o) throws Exception { 49 return patheticDeepCopy(o) == o; 50 } 51 52 public static void main(String[] args) throws Exception { 53 if (!isSingleton(Collections.EMPTY_SET)) 54 throw new Exception("EMPTY_SET"); 55 if (!isSingleton(Collections.EMPTY_LIST)) 56 throw new Exception("EMPTY_LIST"); 57 if (!isSingleton(Collections.EMPTY_MAP)) 58 throw new Exception("EMPTY_MAP"); 59 } 60 }