code: // from gee.cs.oswego.edu/home/jsr166/jsr166
  
  package jsr166tests.jtreg.util.concurrent.ConcurrentMap;
  
  /*
   * 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 6312056 4155650 4294891 4904074
   * @summary Reasonable things should happen if mutating while iterating.
   */
  
  import edu.stanford.ppl.concurrent.SnapTreeMap;
  
  import java.util.*;
  import java.util.concurrent.*;
  
  public class ConcurrentModification {
      static volatile int passed = 0, failed = 0;
  
      static void fail(String msg) {
          failed++;
          new AssertionError(msg).printStackTrace();
      }
  
      static void unexpected(Throwable t) {
          failed++;
          t.printStackTrace();
      }
  
      static void check(boolean condition, String msg) {
          if (condition)
              passed++;
          else
              fail(msg);
      }
  
      static void check(boolean condition) {
          check(condition, "Assertion failed");
      }
  
      private static void test(ConcurrentMap<Integer, Integer> m)
      {
          try {
              m.clear();
              check(m.isEmpty());
              m.put(1,2);
              Iterator<Map.Entry<Integer,Integer>> it = m.entrySet().iterator();
              if (it.hasNext()) {
                  m.remove(1); // sneaky
                  Map.Entry<Integer, Integer> e = it.next();
                  check(m.isEmpty());
                  check(e.getKey() == 1);
                  check(e.getValue() == 2);
              }
          } catch (Throwable t) {unexpected(t);}
  
          try {
              m.clear();
              check(m.isEmpty());
              m.put(1,2);
              Iterator<Map.Entry<Integer,Integer>> it = m.entrySet().iterator();
              if (it.hasNext()) {
                  m.put(1,3); // sneaky
                  Map.Entry<Integer, Integer> e = it.next();
                  check(e.getKey() == 1);
                  check(e.getValue() == 2 || e.getValue() == 3);
                  if (m instanceof ConcurrentHashMap) {
                      e.setValue(4);
                      check(m.get(1) == 4);
                  }
              }
          } catch (Throwable t) {unexpected(t);}
      }
  
      public static void main(String[] args) {
          test(new ConcurrentHashMap<Integer,Integer>());
          test(new ConcurrentSkipListMap<Integer,Integer>());
          test(new SnapTreeMap<Integer,Integer>());
  
          System.out.printf("%nPassed = %d, failed = %d%n%n", passed, failed);
          if (failed > 0) throw new Error("Some tests failed");
      }
  }
  