Filtering Enumeration : Enumerator « Collections Data Structure « Java

Filtering Enumeration


 * The utillib library.
 * More information is available at
 * Copyright (C) 2003 Alexander Maryanovsky.
 * All rights reserved.
 * The utillib library is free software; you can redistribute
 * it and/or modify it under the terms of the GNU Lesser General Public License
 * as published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 * The utillib library is distributed in the hope that it will
 * be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
 * General Public License for more details.
 * You should have received a copy of the GNU Lesser General Public License
 * along with utillib library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

import java.util.Enumeration;
import java.util.NoSuchElementException;

 * An implementation of the <code>Enumeration</code> interface which delegates
 * to another <code>Enumeration</code>, but only returns elements which pass
 * the {@link #accept(Object)} method.

public abstract class FilteringEnumeration implements Enumeration{

   * The delegate enumeration.

  private final Enumeration delegate;

   * The next element we'll return. This is set by the <code>findNext</code>
   * method.

  private Object next = null;

   * Creates a new <code>FilteringEnumeration</code> object with the specified
   * delegate.

  public FilteringEnumeration(Enumeration delegate){
    this.delegate = delegate;

   * Finds the next element in the delegate enumeration which passes
   * <code>accept</code> and puts it in <code>next</code>.

  private void findNext(){
    if (next != null)

    while (delegate.hasMoreElements()){
      Object element = delegate.nextElement();
      if (accept(element)){
        next = element;

   * Returns whether there are more elements in this <code>Enumeration</code>.

  public boolean hasMoreElements(){

    return next != null;

   * Returns the next element in the delegate enumeration which passes the
   * <code>accept</code> method.

  public Object nextElement() throws NoSuchElementException{

    if (next == null)
      throw new NoSuchElementException();

    Object result = next;
    next = null;
    return result;

   * Returns whether the specified object passes the filter.

  public abstract boolean accept(Object element);



Related examples in the same category

1.Wrapping an Iterator around an Enumeration
2.A GOF Adapter to make instances of old Enumeration interface behave like new Iterator interface
3.A more robust enumeration systemA more robust enumeration system
4.ListOfFiles implements Enumeration
5.Treat an Enumeration as an Iterable
6.Support for breadth-first enumerating.
7.Empty Enumeration
8.Single Item Enumeration
9.Enumeration interface which enumerates the items of an arrayEnumeration interface which enumerates the items of an array
10.An enumeration that iterates over an array.An enumeration that iterates over an array.
11.Concatenates the content of two enumerations into one.
12.Removes all nulls from the input enumeration.
13.Filters some elements out from the input enumeration.
14.For each element of the input enumeration asks the Processor to provide a replacement