code: // from gee.cs.oswego.edu/home/jsr166/jsr166
  
  package jsr166tests.jtreg.util.Collections;
  
  /*
   * Copyright 2003-2007 Sun Microsystems, Inc.  All Rights Reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.
   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
   * CA 95054 USA or visit www.sun.com if you need additional information or
   * have any questions.
   */
  
  /*
   * @test
   * @bug     4809442 6366832 4974878 6372554 4890211 6483125
   * @summary Basic test for Collections.reverseOrder
   * @author  Josh Bloch, Martin Buchholz
   */
  
  import java.util.*;
  import java.io.*;
  
  public class ReverseOrder2 {
      final static int N = 100;
  
      static void realMain(String[] args) throws Throwable {
          check(Collections.reverseOrder()
                == Collections.reverseOrder(null));
  
          check(Collections.reverseOrder()
                == reincarnate(Collections.reverseOrder()));
  
          check(Collections.reverseOrder(Collections.reverseOrder(cmp))
                == cmp);
  
          equal(Collections.reverseOrder(cmp),
                Collections.reverseOrder(cmp));
  
          equal(Collections.reverseOrder(cmp).hashCode(),
                Collections.reverseOrder(cmp).hashCode());
  
          check(Collections.reverseOrder(cmp).hashCode() !=
                cmp.hashCode());
  
          test(new ArrayList<String>());
          test(new LinkedList<String>());
          test2(new ArrayList<Integer>());
          test2(new LinkedList<Integer>());
      }
  
      static void test(List<String> list) {
          for (int i = 0; i < N; i++)
              list.add(String.valueOf(i));
          Collections.shuffle(list);
          Collections.sort(list, Collections.reverseOrder(cmp));
          equal(list, golden);
      }
  
      private static Comparator<String> cmp = new Comparator<String> () {
          public int compare(String s1, String s2) {
              int i1 = Integer.parseInt(s1);
              int i2 = Integer.parseInt(s2);
              return (i1 < i2 ? Integer.MIN_VALUE : (i1 == i2 ? 0 : 1));
          }
      };
  
      private final static List<String> golden = new ArrayList<String>(N);
      static {
          for (int i = N-1; i >= 0; i--)
              golden.add(String.valueOf(i));
      }
  
      static void test2(List<Integer> list) {
          for (int i = 0; i < N; i++)
              list.add(i);
          Collections.shuffle(list);
          Collections.sort(list, Collections.reverseOrder(null));
          equal(list, golden2);
      }
  
      private final static List<Integer> golden2 = new ArrayList<Integer>(N);
      static {
          for (int i = N-1; i >= 0; i--)
              golden2.add(i);
      }
  
      //--------------------- Infrastructure ---------------------------
      static volatile int passed = 0, failed = 0;
      static void pass() {passed++;}
      static void fail() {failed++; Thread.dumpStack();}
      static void fail(String msg) {System.out.println(msg); fail();}
      static void unexpected(Throwable t) {failed++; t.printStackTrace();}
      static void check(boolean cond) {if (cond) pass(); else fail();}
      static void equal(Object x, Object y) {
          if (x == null ? y == null : x.equals(y)) pass();
          else fail(x + " not equal to " + y);}
      public static void main(String[] args) throws Throwable {
          try {realMain(args);} catch (Throwable t) {unexpected(t);}
          System.out.printf("%nPassed = %d, failed = %d%n%n", passed, failed);
          if (failed > 0) throw new AssertionError("Some tests failed");}
      static byte[] serializedForm(Object obj) {
          try {
              ByteArrayOutputStream baos = new ByteArrayOutputStream();
              new ObjectOutputStream(baos).writeObject(obj);
              return baos.toByteArray();
          } catch (IOException e) {throw new RuntimeException(e);}}
      static Object readObject(byte[] bytes)
          throws IOException, ClassNotFoundException {
          InputStream is = new ByteArrayInputStream(bytes);
          return new ObjectInputStream(is).readObject();}
      @SuppressWarnings("unchecked")
      static <T> T reincarnate(T obj) {
          try {return (T) readObject(serializedForm(obj));}
          catch (Exception e) {throw new RuntimeException(e);}}
  }
  