gomp-20050608-branch/libjava/classpath/gnu/javax/swing/text/html/parser/support/low/Queue.java

   1 /* Queue.java -- a token queue.
   2    Copyright (C) 2005 Free Software Foundation, Inc.
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  19 02110-1301 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37
  38
  39 package gnu.javax.swing.text.html.parser.support.low;
  40
  41 import java.util.Arrays;
  42
  43 /**
  44  * A token queue.
  45  * @author Audrius Meskauskas, Lithuania (AudriusA@Bioinformatics.org)
  46  */
  47 public class Queue
  48 {
  49   Token[] m = new Token[ 64 ];
  50   int a = 0;
  51   int b = 0;
  52
  53   /**
  54    * True for the empty queue.
  55    */
  56   public boolean isEmpty()
  57   {
  58     return size() == 0;
  59   }
  60
  61   /**
  62    *  Add this trace to the end of the queue.
  63    */
  64   public void add(Token u)
  65   {
  66     if (a < m.length)
  67       {
  68         m [ a ] = u;
  69         a++;
  70       }
  71     else // The end of array has been reached.
  72       {
  73         if (b > 0) // If some elements were deleted from the start of the queue, shift.
  74           {
  75             int d = b;
  76             System.arraycopy(m, b, m, 0, a - b);
  77             b = b - d;
  78             a = a - d;
  79             m [ a ] = u;
  80             a++;
  81           }
  82         else // Enlarge the queue, doubling the size.
  83           {
  84             int n = m.length * 2;
  85             Token[] nm = new Token[ 2 * n ];
  86             System.arraycopy(m, 0, nm, 0, m.length);
  87             Arrays.fill(m, null);
  88
  89             nm [ a ] = u;
  90             m = nm;
  91             a++;
  92           }
  93       }
  94   }
  95
  96   /**
  97    * Clear the queue.
  98    */
  99   public void clear()
 100   {
 101     a = b = 0;
 102     Arrays.fill(m, null);
 103   }
 104
 105   /**
 106    * Read the value ahead. 0 is the value that will be returned with
 107    * the following next. This method does not remove values from the
 108    * queue. To test if there is enough tokens in the queue, size() must
 109    * be checked before calling this method.
 110    */
 111   public Token get(int ahead)
 112   {
 113     int p = b + ahead;
 114     if (p < a)
 115       return m [ p ];
 116     else
 117       throw new ArrayIndexOutOfBoundsException("Not enough tokens");
 118   }
 119
 120   /**
 121    * Read the oldest value from the queue and remove this value from
 122    * the queue.
 123    */
 124   public Token next()
 125   {
 126     if (a == b)
 127       throw new ArrayIndexOutOfBoundsException("queue empty");
 128
 129     Token r = m [ b ];
 130     m [ b ] = null;
 131     b++;
 132     return r;
 133   }
 134
 135   /**
 136    * Size of the queue.
 137    */
 138   public int size()
 139   {
 140     return a - b;
 141   }
 142 }