001    /* ContentModel.java --
002       Copyright (C) 2005 Free Software Foundation, Inc.
003    
004    This file is part of GNU Classpath.
005    
006    GNU Classpath is free software; you can redistribute it and/or modify
007    it under the terms of the GNU General Public License as published by
008    the Free Software Foundation; either version 2, or (at your option)
009    any later version.
010    
011    GNU Classpath is distributed in the hope that it will be useful, but
012    WITHOUT ANY WARRANTY; without even the implied warranty of
013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014    General Public License for more details.
015    
016    You should have received a copy of the GNU General Public License
017    along with GNU Classpath; see the file COPYING.  If not, write to the
018    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019    02110-1301 USA.
020    
021    Linking this library statically or dynamically with other modules is
022    making a combined work based on this library.  Thus, the terms and
023    conditions of the GNU General Public License cover the whole
024    combination.
025    
026    As a special exception, the copyright holders of this library give you
027    permission to link this library with independent modules to produce an
028    executable, regardless of the license terms of these independent
029    modules, and to copy and distribute the resulting executable under
030    terms of your choice, provided that you also meet, for each linked
031    independent module, the terms and conditions of the license of that
032    module.  An independent module is a module which is not derived from
033    or based on this library.  If you modify this library, you may extend
034    this exception to your version of the library, but you are not
035    obligated to do so.  If you do not wish to do so, delete this
036    exception statement from your version. */
037    
038    
039    package javax.swing.text.html.parser;
040    
041    import gnu.javax.swing.text.html.parser.models.transformer;
042    
043    import java.io.Serializable;
044    
045    import 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     */
072    public 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    }