001/* ContentModel.java --
002   Copyright (C) 2005 Free Software Foundation, Inc.
003
004This file is part of GNU Classpath.
005
006GNU Classpath is free software; you can redistribute it and/or modify
007it under the terms of the GNU General Public License as published by
008the Free Software Foundation; either version 2, or (at your option)
009any later version.
010
011GNU Classpath is distributed in the hope that it will be useful, but
012WITHOUT ANY WARRANTY; without even the implied warranty of
013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014General Public License for more details.
015
016You should have received a copy of the GNU General Public License
017along with GNU Classpath; see the file COPYING.  If not, write to the
018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
01902110-1301 USA.
020
021Linking this library statically or dynamically with other modules is
022making a combined work based on this library.  Thus, the terms and
023conditions of the GNU General Public License cover the whole
024combination.
025
026As a special exception, the copyright holders of this library give you
027permission to link this library with independent modules to produce an
028executable, regardless of the license terms of these independent
029modules, and to copy and distribute the resulting executable under
030terms of your choice, provided that you also meet, for each linked
031independent module, the terms and conditions of the license of that
032module.  An independent module is a module which is not derived from
033or based on this library.  If you modify this library, you may extend
034this exception to your version of the library, but you are not
035obligated to do so.  If you do not wish to do so, delete this
036exception statement from your version. */
037
038
039package javax.swing.text.html.parser;
040
041import gnu.javax.swing.text.html.parser.models.transformer;
042
043import java.io.Serializable;
044
045import java.util.Vector;
046
047/**
048 * A representation of the element content. The instances of this class
049 * can be arranged into the linked list, representing a BNF expression.
050 * The content model is constructed as a branched tree structure in the
051 * following way:
052 * <pre>
053 * a = new ContentModel('+', A, null); // a reprensents A+
054 * b = new ContentModel('&amp;', B, a); // b represents B &amp; A+
055 * c = new ContentModel('*', b, null); // c represents ( B &amp; A+) *
056 * d = new ContentModel('|', new ContentModel('*', A, null),
057 *          new ContentModel('?', B, null)); // d represents ( A* | B? )
058 * </pre>
059 * where the valid operations are:
060 * <ul>
061 * <li><code>E* </code> E occurs zero or more times</li>
062 * <li><code>E+ </code> E occurs one or more times</li>
063 * <li><code>E? </code> E occurs once or not atl all</li>
064 * <li><code>A,B</code> A occurs before B</li>
065 * <li><code>A|B</code> both A and B are permitted in any order.
066 * The '|' alone does not permit the repetetive occurence of A or B
067 * (use <code>(A|B)*</code>.</li>
068 * <li><code>A&amp;B</code> both A and B must occur once (in any order)</li>
069 * </ul>
070 * @author Audrius Meskauskas, Lithuania (AudriusA@Bioinformatics.org)
071 */
072public final class ContentModel
073  implements Serializable
074{
075  /** Use serialVersionUID for interoperability. */
076  private static final long serialVersionUID = -1130825523866321257L;
077
078  /**
079   * The next content model model ( = pointer to the next element of
080   * the linked list) for the binary expression (',','&amp;' or '|'). Null
081   * for the last element in the list.
082   */
083  public ContentModel next;
084
085  /**
086   * The document content, containing either Element or the enclosed
087   * content model (that would be in the parentheses in BNF expression).
088   */
089  public Object content;
090
091  /**
092   * Specifies the BNF operation between this node and the node,
093   * stored in the field <code>next</code> (or for this node, if it is
094   * an unary operation.
095   */
096  public int type;
097
098  /**
099   * 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<Element> elements)
155  {
156    ContentModel c = this;
157
158    while (c != null)
159      {
160        // FIXME: correct?
161        if (c.content instanceof Element)
162          elements.add((Element) c.content);
163        c = c.next;
164      }
165  }
166
167  /**
168   * Checks if the content model matches an empty input stream.
169   * The empty content is created using SGML DTD keyword EMPTY.
170   * The empty model is a model with the content field equal to null.
171   *
172   * @return true if the content field is equal to null.
173   */
174  public boolean empty()
175  {
176    return content == null;
177  }
178
179  /**
180   * Get the element, stored in the <code>next.content</code>.
181   * The method is programmed as the part of the standard API, but not
182   * used in this implementation.
183   * @return the value of the field <code>next</code>.
184   */
185  public Element first()
186  {
187    return (Element) next.content;
188  }
189
190  /**
191   * Checks if this object can potentially be the first token in the
192   * ContenModel list. The method is programmed as the part of the
193   *  standard API, but not used in this implementation.
194   */
195  public boolean first(Object token)
196  {
197    ContentModel c = this;
198    while (c.next != null)
199      {
200        if (c.content != null && c.content.toString().equals(token.toString()) &&
201            c.type != ','
202           )
203
204          // Agree if the operation with the preceeding element
205          // is not the comma operation.
206          return true;
207        c = c.next;
208      }
209    return false;
210  }
211
212  /**
213   * Returns a string representation (an expression) of this content model.
214   * The expression has BNF-like syntax, except the absence of the
215   * unary operator is additionally indicated by " ' ". It is
216   * advisable to check the created models for correctness using this
217   * method.
218   */
219  public String toString()
220  {
221    return transformer.transform(this).toString();
222  }
223}