libjava/classpath/javax/swing/text/html/parser/ContentModel.java

/* ContentModel.java --
   Copyright (C) 2005 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
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02110-1301 USA.

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making a combined work based on this library.  Thus, the terms and
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permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
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package javax.swing.text.html.parser;

import gnu.javax.swing.text.html.parser.models.transformer;

import java.io.Serializable;

import java.util.Vector;

/**
 * A representation of the element content. The instances of this class
 * can be arranged into the linked list, representing a BNF expression.
 * The content model is constructed as a branched tree structure in the
 * following way:
 * <pre>
 * a = new ContentModel('+', A, null); // a reprensents A+
 * b = new ContentModel('&amp;', B, a); // b represents B &amp; A+
 * c = new ContentModel('*', b, null); // c represents ( B &amp; A+) *
 * d = new ContentModel('|', new ContentModel('*', A, null),
 *          new ContentModel('?', B, null)); // d represents ( A* | B? )
 * </pre>
 * where the valid operations are:
 * <ul>
 * <li><code>E* </code> E occurs zero or more times</li>
 * <li><code>E+ </code> E occurs one or more times</li>
 * <li><code>E? </code> E occurs once or not atl all</li>
 * <li><code>A,B</code> A occurs before B</li>
 * <li><code>A|B</code> both A and B are permitted in any order.
 * The '|' alone does not permit the repetetive occurence of A or B
 * (use <code>(A|B)*</code>.</li>
 * <li><code>A&amp;B</code> both A and B must occur once (in any order)</li>
 * </ul>
 * @author Audrius Meskauskas, Lithuania (AudriusA@Bioinformatics.org)
 */
public final class ContentModel
  implements Serializable
{
  /** Use serialVersionUID for interoperability. */
  private static final long serialVersionUID = -1130825523866321257L;

  /**
   * The next content model model ( = pointer to the next element of
   * the linked list) for the binary expression (',','&amp;' or '|'). Null
   * for the last element in the list.
   */
  public ContentModel next;

  /**
   * The document content, containing either Element or the enclosed
   * content model (that would be in the parentheses in BNF expression).
   */
  public Object content;

  /**
   * Specifies the BNF operation between this node and the node,
   * stored in the field <code>next</code> (or for this node, if it is
   * an unary operation.
   */
  public int type;

  /**
   * Create a content model initializing all fields to default values.
   */
  public ContentModel()
  {
    // Nothing to do here.
  }

  /**
   * Create a content model, consisting of the single element.
   * Examples:
   *<code>
   * a = new ContentModel('+', A, null); // a reprensents A+
   * b = new ContentModel('&amp;', B, a);    // b represents  B &amp; A+
   * c = new ContentModel('*', b, null); // c represents  ( B &amp; A+) *
   * d = new ContentModel('|', A,
   *    new ContentModel('?',b, null);
   *     // d represents
   * </code>
   */
  public ContentModel(Element a_content)
  {
    content = a_content;
  }

  /**
   * Create a content model, involving expression of the given type.
   * @param a_type The expression operation type ('*','?' or '+'
   * @param a_content The content for that the expression is applied.
   */
  public ContentModel(int a_type, ContentModel a_content)
  {
    content = a_content;
    type = a_type;
  }

  /**
   * Create a content model, involving binary expression of the given type.
   * @param a_type The expression operation type ( ',', '|' or '&amp;').
   * @param a_content The content of the left part of the expression.
   * @param a_next The content model, representing the right part of the
   * expression.
   */
  public ContentModel(int a_type, Object a_content, ContentModel a_next)
  {
    content = a_content;
    type = a_type;
    next = a_next;
  }

  /**
   * Adds all list elements to the given vector, ignoring the
   * operations between the elements. The old vector values are not
   * discarded.
   * @param elements - a vector to add the values to.
   */
  public void getElements(Vector<Element> elements)
  {
    ContentModel c = this;

    while (c != null)
      {
        // FIXME: correct?
        if (c.content instanceof Element)
          elements.add((Element) c.content);
        c = c.next;
      }
  }

  /**
   * Checks if the content model matches an empty input stream.
   * The empty content is created using SGML DTD keyword EMPTY.
   * The empty model is a model with the content field equal to null.
   *
   * @return true if the content field is equal to null.
   */
  public boolean empty()
  {
    return content == null;
  }

  /**
   * Get the element, stored in the <code>next.content</code>.
   * The method is programmed as the part of the standard API, but not
   * used in this implementation.
   * @return the value of the field <code>next</code>.
   */
  public Element first()
  {
    return (Element) next.content;
  }

  /**
   * Checks if this object can potentially be the first token in the
   * ContenModel list. The method is programmed as the part of the
   *  standard API, but not used in this implementation.
   */
  public boolean first(Object token)
  {
    ContentModel c = this;
    while (c.next != null)
      {
        if (c.content != null && c.content.toString().equals(token.toString()) &&
            c.type != ','
           )

          // Agree if the operation with the preceeding element
          // is not the comma operation.
          return true;
        c = c.next;
      }
    return false;
  }

  /**
   * Returns a string representation (an expression) of this content model.
   * The expression has BNF-like syntax, except the absence of the
   * unary operator is additionally indicated by " ' ". It is
   * advisable to check the created models for correctness using this
   * method.
   */
  public String toString()
  {
    return transformer.transform(this).toString();
  }
}