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/* Queue.java -- a token queue.

   Copyright (C) 2005 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify

it under the terms of the GNU General Public License as published by

the Free Software Foundation; either version 2, or (at your option)

any later version.

GNU Classpath 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 for more details.

You should have received a copy of the GNU General Public License

along with GNU Classpath; see the file COPYING.  If not, write to the

Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA

02110-1301 USA.

Linking this library statically or dynamically with other modules is

making a combined work based on this library.  Thus, the terms and

conditions of the GNU General Public License cover the whole

combination.

As a special exception, the copyright holders of this library give you

permission to link this library with independent modules to produce an

executable, regardless of the license terms of these independent

modules, and to copy and distribute the resulting executable under

terms of your choice, provided that you also meet, for each linked

independent module, the terms and conditions of the license of that

module.  An independent module is a module which is not derived from

or based on this library.  If you modify this library, you may extend

this exception to your version of the library, but you are not

obligated to do so.  If you do not wish to do so, delete this

exception statement from your version. */

package gnu.javax.swing.text.html.parser.support.low;

import java.util.Arrays;

/**

 * A token queue.

 * @author Audrius Meskauskas, Lithuania (AudriusA@Bioinformatics.org)

 */

public class Queue

{

  Token[] m = new Token[ 64 ];

  int a = 0;

  int b = 0;

  /**

   * True for the empty queue.

   */

  public boolean isEmpty()

  {

    return size() == 0;

  }

  /**

   *  Add this trace to the end of the queue.

   */

  public void add(Token u)

  {

    if (a < m.length)

      {

        m [ a ] = u;

        a++;

      }

    else // The end of array has been reached.

      {

        if (b > 0) // If some elements were deleted from the start of the queue, shift.

          {

            int d = b;

            System.arraycopy(m, b, m, 0, a - b);

            b = b - d;

            a = a - d;

            m [ a ] = u;

            a++;

          }

        else // Enlarge the queue, doubling the size.

          {

            int n = m.length * 2;

            Token[] nm = new Token[ 2 * n ];

            System.arraycopy(m, 0, nm, 0, m.length);

            Arrays.fill(m, null);

            nm [ a ] = u;

            m = nm;

            a++;

          }

      }

  }

  /**

   * Clear the queue.

   */

  public void clear()

  {

    a = b = 0;

    Arrays.fill(m, null);

  }

  /**

   * Read the value ahead. 0 is the value that will be returned with

   * the following next. This method does not remove values from the

   * queue. To test if there is enough tokens in the queue, size() must

   * be checked before calling this method.

   */

  public Token get(int ahead)

  {

    int p = b + ahead;

    if (p < a)

      return m [ p ];

    else

      throw new ArrayIndexOutOfBoundsException("Not enough tokens");

  }

  /**

   * Read the oldest value from the queue and remove this value from

   * the queue.

   */

  public Token next()

  {

    if (a == b)

      throw new ArrayIndexOutOfBoundsException("queue empty");

    Token r = m [ b ];

    m [ b ] = null;

    b++;

    return r;

  }

  /**

   * Size of the queue.

   */

  public int size()

  {

    return a - b;

  }

}