Create a typesafe filter of an unchecked iterator. : Generic Collection « Generics « Java

Create a typesafe filter of an unchecked iterator.

 * Copyright 1997-2007 Sun Microsystems, Inc. All rights reserved.
 * The contents of this file are subject to the terms of either the GNU
 * General Public License Version 2 only ("GPL") or the Common
 * Development and Distribution License("CDDL") (collectively, the
 * "License"). You may not use this file except in compliance with the
 * License. You can obtain a copy of the License at
 * or nbbuild/licenses/CDDL-GPL-2-CP. See the License for the
 * specific language governing permissions and limitations under the
 * License.  When distributing the software, include this License Header
 * Notice in each file and include the License file at
 * nbbuild/licenses/CDDL-GPL-2-CP.  Sun designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Sun in the GPL Version 2 section of the License file that
 * accompanied this code. If applicable, add the following below the
 * License Header, with the fields enclosed by brackets [] replaced by
 * your own identifying information:
 * "Portions Copyrighted [year] [name of copyright owner]"
 * Contributor(s):
 * The Original Software is NetBeans. The Initial Developer of the Original
 * Software is Sun Microsystems, Inc. Portions Copyright 1997-2006 Sun
 * Microsystems, Inc. All Rights Reserved.
 * If you wish your version of this file to be governed by only the CDDL
 * or only the GPL Version 2, indicate your decision by adding
 * "[Contributor] elects to include this software in this distribution
 * under the [CDDL or GPL Version 2] license." If you do not indicate a
 * single choice of license, a recipient has the option to distribute
 * your version of this file under either the CDDL, the GPL Version 2 or
 * to extend the choice of license to its licensees as provided above.
 * However, if you add GPL Version 2 code and therefore, elected the GPL
 * Version 2 license, then the option applies only if the new code is
 * made subject to such option by the copyright holder.

import java.util.Iterator;
import java.util.NoSuchElementException;

 * @since 4.37
 * @author Jaroslav Tulach

public class Utils {
   * Create a typesafe filter of an unchecked iterator. {@link Iterator#remove}
   * will work if it does in the unchecked iterator.
   * @param rawIterator
   *          an unchecked iterator
   * @param type
   *          the desired enumeration type
   * @param strict
   *          if false, elements which are not null but not assignable to the
   *          requested type are omitted; if true, {@link ClassCastException}
   *          may be thrown from an iterator operation
   * @return an iterator guaranteed to contain only objects of the requested
   *         type (or null)
  public static <E> Iterator<E> checkedIteratorByFilter(Iterator rawIterator, final Class<E> type,
      final boolean strict) {
    return new CheckedIterator<E>(rawIterator) {
      protected boolean accept(Object o) {
        if (o == null) {
          return true;
        } else if (type.isInstance(o)) {
          return true;
        } else if (strict) {
          throw new ClassCastException(o + " was not a " + type.getName()); // NOI18N
        } else {
          return false;


abstract class CheckedIterator<E> implements Iterator<E> {

  static final Object WAITING = new Object();

  private final Iterator it;

  private Object next = WAITING;

  public CheckedIterator(Iterator it) { = it;

  protected abstract boolean accept(Object o);

  public boolean hasNext() {
    if (next != WAITING) {
      return true;
    while (it.hasNext()) {
      next =;
      if (accept(next)) {
        return true;
    next = WAITING;
    return false;

  public E next() {
    if (next == WAITING && !hasNext()) {
      throw new NoSuchElementException();
    assert next != WAITING;
    // type-checking is done by accept()
    E x = (E) next;
    next = WAITING;
    return x;

  public void remove() {



Related examples in the same category

1.Creating a Type-Specific List
2.A list declared to hold objects of a type T can also hold objects that extend from T.
3.A value retrieved from a type-specific list does not need to be casted
4.Generic ArrayListGeneric ArrayList
5.Generic Data Structure
6.Unchecked Example
7.Generic StackGeneric Stack
8.Enum and GenericEnum and Generic
9.Generic HashMapGeneric HashMap
10.Foreach and generic data structureForeach and generic data structure
11.Pre generics example that uses a collection.Pre generics example that uses a collection.
12.Data structure and collections: Modern, generics version.Data structure and collections: Modern, generics version.
13.Java generic: Generics and arrays.
14.Collections and Data structure: the generic wayCollections and Data structure: the generic way
15.The GenStack Class
16.Create a typesafe copy of a raw set.
17.Create a typesafe copy of a raw list.
18.Create a typesafe copy of a raw map.
19.Create a typesafe view over an underlying raw set.
20.Create a typesafe view over an underlying raw map.
21.Create a typesafe filter of an unchecked enumeration.
22.Circular Object Buffer
23.A collection that do not hold stored elements in memory, but serialize it into a file
24.Generic Triple structure
25.Generic Pair
26.A generic bag of properties used to store properties that apply to a specific target.
27.Pool container