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 }