code: // from gee.cs.oswego.edu/home/jsr166/jsr166
  
  package jsr166tests.jtreg.util.Deque;
  
  /*
   * Copyright 2005 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 6324846
   * @summary Deque implementations must behave isomorphically
   * @author Martin Buchholz
   */
  
  import java.util.*;
  import java.util.concurrent.*;
  
  public class ChorusLine {
      private interface Tweaker {
          void run(Deque<Integer> deq);
      }
  
      private final static Tweaker[] tweakers = {
          new Tweaker() { public void run(Deque<Integer> deq) {
              for (int i = 0; i < 7; i++)
                  deq.addLast(i);
              deq.removeFirst();
              deq.removeFirst();
              deq.addLast(7);
              deq.addLast(8);
              Iterator<Integer> it = deq.descendingIterator();
              equal(it.next(), 8);
              it.remove();
  
              try {it.remove();}
              catch (IllegalStateException e) {pass();}
              catch (Throwable t) {unexpected(t);}
  
              deq.addLast(9);
              it = deq.descendingIterator();
              equal(it.next(), 9);
              equal(it.next(), 7);
              it.remove();
  
              try {it.remove();}
              catch (IllegalStateException e) {pass();}
              catch (Throwable t) {unexpected(t);}
  
              equal(it.next(), 6);
  
              System.out.println(deq);
          }},
          new Tweaker() { public void run(Deque<Integer> deq) {
              deq.clear();
              check(deq.isEmpty());
              check(deq.size() == 0);
              check(! deq.iterator().hasNext());
              check(! deq.descendingIterator().hasNext());
  
              try {deq.iterator().next(); fail();}
              catch (NoSuchElementException e) {pass();}
              catch (Throwable t) {unexpected(t);}
  
              try {deq.descendingIterator().next(); fail();}
              catch (NoSuchElementException e) {pass();}
              catch (Throwable t) {unexpected(t);}
          }},
          new Tweaker() { public void run(Deque<Integer> deq) {
              for (int i = 0; i < 11; i++)
                  deq.add(i);
              Iterator<Integer> it = deq.iterator();
              equal(it.next(), 0);
              equal(it.next(), 1);
              it.remove();
              deq.addFirst(-1);
              deq.addFirst(-2);
              it = deq.iterator();
              equal(it.next(), -2);
              equal(it.next(), -1);
              equal(it.next(), 0);
              it.remove();
  
              it = deq.descendingIterator();
  
              try {it.remove(); fail();}
              catch (IllegalStateException e) {pass();}
              catch (Throwable t) {unexpected(t);}
  
              equal(it.next(), 10);
              it.remove();
  
              try {it.remove(); fail();}
              catch (IllegalStateException e) {pass();}
              catch (Throwable t) {unexpected(t);}
  
              equal(it.next(), 9);
              equal(it.next(), 8);
              it.remove();
              System.out.println(deq);
          }},
          new Tweaker() { public void run(Deque<Integer> deq) {
              while (deq.size() > 1) {
                  Iterator<Integer> it = deq.iterator();
                  it.next(); it.remove();
                  it = deq.descendingIterator();
                  it.next(); it.remove();
              }
              System.out.println(deq);
          }}};
  
      private static void realMain(String[] args) throws Throwable {
          Collection<Deque<Integer>> deqs = new ArrayDeque<Deque<Integer>>(3);
          deqs.add(new ArrayDeque<Integer>());
          deqs.add(new LinkedList<Integer>());
          deqs.add(new LinkedBlockingDeque<Integer>());
  
          equal(deqs);
  
          for (Tweaker tweaker : tweakers) {
              for (Deque<Integer> deq : deqs)
                  tweaker.run(deq);
              equal(deqs);
          }
      }
  
      private static void equal(Iterable<Deque<Integer>> deqs) {
          Deque<Integer> prev = null;
          for (Deque<Integer> deq : deqs) {
              if (prev != null) {
                  equal(prev.isEmpty(), deq.isEmpty());
                  equal(prev.size(), deq.size());
                  equal(prev.toString(), deq.toString());
              }
              prev = deq;
          }
  
          Deque<Iterator<Integer>> its = new ArrayDeque<Iterator<Integer>>();
          for (Deque<Integer> deq : deqs)
              its.addLast(deq.iterator());
          equal(its);
  
          Deque<Iterator<Integer>> dits = new ArrayDeque<Iterator<Integer>>();
          for (Deque<Integer> deq : deqs)
              dits.addLast(deq.descendingIterator());
          equal(dits);
      }
  
      private static void equal(Deque<Iterator<Integer>> its) {
          Iterator<Integer> it0 = its.remove();
          while (it0.hasNext()) {
              Integer i = it0.next();
              for (Iterator<Integer> it : its)
                  equal(it.next(), i);
          }
          for (Iterator<Integer> it : its) {
              check(! it.hasNext());
  
              try {it.next(); fail();}
              catch (NoSuchElementException e) {pass();}
              catch (Throwable t) {unexpected(t);}
          }
      }
  
      //--------------------- 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");}
  }
  