Source for gnu.javax.swing.text.html.parser.support.low.Queue

   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: }