gomp-20050608-branch/libjava/classpath/javax/swing/text/html/parser/ContentModel.java

   1 /* ContentModel.java --
   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 javax.swing.text.html.parser;
  40
  41 import gnu.javax.swing.text.html.parser.models.transformer;
  42
  43 import java.io.Serializable;
  44
  45 import java.util.Vector;
  46
  47 /**
  48  * A representation of the element content. The instances of this class
  49  * can be arranged into the linked list, representing a BNF expression.
  50  * The content model is constructed as a branched tree structure in the
  51  * following way:
  52  * <pre>
  53  * a = new ContentModel('+', A, null); // a reprensents A+
  54  * b = new ContentModel('&amp;', B, a); // b represents B &amp; A+
  55  * c = new ContentModel('*', b, null); // c represents ( B &amp; A+) *
  56  * d = new ContentModel('|', new ContentModel('*', A, null),
  57  *          new ContentModel('?', B, null)); // d represents ( A* | B? )
  58  * </pre>
  59  * where the valid operations are:
  60  * <ul>
  61  * <li><code>E* </code> E occurs zero or more times</li>
  62  * <li><code>E+ </code> E occurs one or more times</li>
  63  * <li><code>E? </code> E occurs once or not atl all</li>
  64  * <li><code>A,B</code> A occurs before B</li>
  65  * <li><code>A|B</code> both A and B are permitted in any order.
  66  * The '|' alone does not permit the repetetive occurence of A or B
  67  * (use <code>(A|B)*</code>.</li>
  68  * <li><code>A&amp;B</code> both A and B must occur once (in any order)</li>
  69  * </ul>
  70  * @author Audrius Meskauskas, Lithuania (AudriusA@Bioinformatics.org)
  71  */
  72 public final class ContentModel
  73   implements Serializable
  74 {
  75   /** Use serialVersionUID for interoperability. */
  76   private static final long serialVersionUID = -1130825523866321257L;
  77
  78   /**
  79    * The next content model model ( = pointer to the next element of
  80    * the linked list) for the binary expression (',','&amp;' or '|'). Null
  81    * for the last element in the list.
  82    */
  83   public ContentModel next;
  84
  85   /**
  86    * The document content, containing either Element or the enclosed
  87    * content model (that would be in the parentheses in BNF expression).
  88    */
  89   public Object content;
  90
  91   /**
  92    * Specifies the BNF operation between this node and the node,
  93    * stored in the field <code>next</code> (or for this node, if it is
  94    * an unary operation.
  95    */
  96   public int type;
  97
  98   /**
  99    * Create a content model initializing all fields to default values.
 100    */
 101   public ContentModel()
 102   {
 103     // Nothing to do here.
 104   }
 105
 106   /**
 107    * Create a content model, consisting of the single element.
 108    * Examples:
 109    *<code>
 110    * a = new ContentModel('+', A, null); // a reprensents A+
 111    * b = new ContentModel('&amp;', B, a);    // b represents  B &amp; A+
 112    * c = new ContentModel('*', b, null); // c represents  ( B &amp; A+) *
 113    * d = new ContentModel('|', A,
 114    *    new ContentModel('?',b, null);
 115    *     // d represents
 116    * </code>
 117    */
 118   public ContentModel(Element a_content)
 119   {
 120     content = a_content;
 121   }
 122
 123   /**
 124    * Create a content model, involving expression of the given type.
 125    * @param a_type The expression operation type ('*','?' or '+'
 126    * @param a_content The content for that the expression is applied.
 127    */
 128   public ContentModel(int a_type, ContentModel a_content)
 129   {
 130     content = a_content;
 131     type = a_type;
 132   }
 133
 134   /**
 135    * Create a content model, involving binary expression of the given type.
 136    * @param a_type The expression operation type ( ',', '|' or '&amp;').
 137    * @param a_content The content of the left part of the expression.
 138    * @param a_next The content model, representing the right part of the
 139    * expression.
 140    */
 141   public ContentModel(int a_type, Object a_content, ContentModel a_next)
 142   {
 143     content = a_content;
 144     type = a_type;
 145     next = a_next;
 146   }
 147
 148   /**
 149    * Adds all list elements to the given vector, ignoring the
 150    * operations between the elements. The old vector values are not
 151    * discarded.
 152    * @param elements - a vector to add the values to.
 153    */
 154   public void getElements(Vector elements)
 155   {
 156     ContentModel c = this;
 157
 158     while (c != null)
 159       {
 160         elements.add(c.content);
 161         c = c.next;
 162       }
 163   }
 164
 165   /**
 166    * Checks if the content model matches an empty input stream.
 167    * The empty content is created using SGML DTD keyword EMPTY.
 168    * The empty model is a model with the content field equal to null.
 169    *
 170    * @return true if the content field is equal to null.
 171    */
 172   public boolean empty()
 173   {
 174     return content == null;
 175   }
 176
 177   /**
 178    * Get the element, stored in the <code>next.content</code>.
 179    * The method is programmed as the part of the standard API, but not
 180    * used in this implementation.
 181    * @return the value of the field <code>next</code>.
 182    */
 183   public Element first()
 184   {
 185     return (Element) next.content;
 186   }
 187
 188   /**
 189    * Checks if this object can potentially be the first token in the
 190    * ContenModel list. The method is programmed as the part of the
 191    *  standard API, but not used in this implementation.
 192    */
 193   public boolean first(Object token)
 194   {
 195     ContentModel c = this;
 196     while (c.next != null)
 197       {
 198         if (c.content != null && c.content.toString().equals(token.toString()) &&
 199             c.type != ','
 200            )
 201
 202           // Agree if the operation with the preceeding element
 203           // is not the comma operation.
 204           return true;
 205         c = c.next;
 206       }
 207     return false;
 208   }
 209
 210   /**
 211    * Returns a string representation (an expression) of this content model.
 212    * The expression has BNF-like syntax, except the absence of the
 213    * unary operator is additionally indicated by " ' ". It is
 214    * advisable to check the created models for correctness using this
 215    * method.
 216    */
 217   public String toString()
 218   {
 219     return transformer.transform(this).toString();
 220   }
 221 }