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[/] [openrisc/] [trunk/] [gnu-dev/] [or1k-gcc/] [libjava/] [classpath/] [gnu/] [java/] [util/] [DoubleEnumeration.java] - Blame information for rev 769

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1 769 jeremybenn
/* gnu.java.util.DoubleEnumeration
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   Copyright (C) 1998, 1999, 2001, 2004 Free Software Foundation, Inc.
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING.  If not, write to the
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Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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02110-1301 USA.
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library.  Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module.  An independent module is a module which is not derived from
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or based on this library.  If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so.  If you do not wish to do so, delete this
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exception statement from your version. */
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package gnu.java.util;
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import java.util.Enumeration;
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import java.util.NoSuchElementException;
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/**
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 * This is a helper class that combines two Enumerations.
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 * It returns the elements of the first Enumeration until it has
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 * no more elements and then returns the elements of the second
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 * Enumeration.<br>
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 *
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 * In the default case:
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 * <pre>
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 * doubleEnum = new DoubleEnumeration(enum1, enum2);
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 * while (doubleEnum.hasMoreElements()) {
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 *    Object o = doubleEnum.nextElement();
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 *    do_something(o);
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 * }
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 * </pre>
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 * it calls hasMoreElements of the Enumerations as few times as
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 * possible.
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 * The references to the Enumerations are cleared as soon as they have no
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 * more elements to help garbage collecting.
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 *
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 * @author Jochen Hoenicke
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 * @author Mark Wielaard (mark@klomp.org)
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 */
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public class DoubleEnumeration<T> implements Enumeration<T>
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{
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  /**
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   * This is true as long as one of the enumerations has more
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   * elements.
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   * Only valid when hasChecked is true.
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   * Set in <code>hasMoreElements()</code>
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   */
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  private boolean hasMore;
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  /**
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   * This is true, if it is sure that hasMore indicates wether there are
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   * more elements.
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   * Set to true in <code>hasMoreElements()</code>.
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   * Set to false in <code>getNextElement()</code>.
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   */
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  private boolean hasChecked;
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  /**
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   * The first enumeration.
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   */
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  private Enumeration<T> e1;
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  /**
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   * The second enumeration.
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   */
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  private Enumeration<T> e2;
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  /**
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   * Creates a new Enumeration combining the given two enumerations.
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   * The enumerations mustn't be accessed by other classes.
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   */
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  public DoubleEnumeration(Enumeration<T> e1, Enumeration<T> e2)
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  {
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    this.e1 = e1;
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    this.e2 = e2;
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    hasChecked = false;
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  }
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  /**
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   * Returns true, if at least one of the two enumerations has more
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   * elements.
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   */
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  public boolean hasMoreElements()
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  {
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    if (hasChecked)
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      return hasMore;
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    hasMore = (e1 != null && e1.hasMoreElements());
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    if (!hasMore) {
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      e1 = e2;
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      e2 = null;
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      hasMore = (e1 != null && e1.hasMoreElements());
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    }
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    hasChecked = true;
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    return hasMore;
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  }
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  /**
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   * Returns the next element.  This returns the next element of the
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   * first enumeration, if it has more elements, otherwise the next
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   * element of the second enumeration. If both enumeration don't have
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   * any elements it throws a <code>NoSuchElementException</code>.
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   */
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  public T nextElement()
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  {
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    if (!hasMoreElements())
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      throw new NoSuchElementException();
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    else {
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      hasChecked = false;
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      return e1.nextElement();
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    }
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  }
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}

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