htmlcollectionimpl.java

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                    if ( collectionMatch( (Element) node, null ) )
                        ++ length;
                    else if ( recurse() )
                        length += getLength( (Element) node );
                }
                node = node.getNextSibling(); 
            }
        }
        return length;
    }
    
        
    /**
     * Recursive function returns the numbered element of a particular type
     * that exist under the top level element. This is a recursive function
     * and the top level element is passed along.
     * <p>
     * Note that this function must call itself with an index and get back both
     * the element (if one was found) and the new index which is decremeneted
     * for any like element found. Since integers are only passed by value,
     * this function makes use of a separate class ({@link CollectionIndex})
     * to hold that index.
     * 
     * @param topLevel Top level element from which to scan
     * @param index The index of the item to retreive
     * @return Number of elements
     * @see CollectionIndex
     */
    private Node item( Element topLevel, CollectionIndex index )
    {
        Node    node;
        Node    result;

        synchronized ( topLevel )
        {
            // Traverse all the childs of the current element in the order
	    // they appear. Count from the index backwards until you reach
	    // matching element with an index of zero. Return that element.
            node = topLevel.getFirstChild();
            while ( node != null )
            {
                // If a particular node is an element (could be HTML or XML),
		// do two things: if it's the one we're looking for, decrease
		// the index and if zero, return this node; at any rate,
		// traverse it's children as well.
                if ( node instanceof Element )
                {
                    if ( collectionMatch( (Element) node, null ) )
                    {
                        if ( index.isZero() )
                            return node;
                        index.decrement();
                    } else if ( recurse() )
                    {
                        result = item( (Element) node, index );
                        if ( result != null )
                            return result;
                    }
                }
                node = node.getNextSibling(); 
            }
        }
        return null;
    }
    
    
    /**
     * Recursive function returns an element of a particular type with the
     * specified name (<TT>id</TT> attribute).
     * 
     * @param topLevel Top level element from which to scan
     * @param name The named element to look for
     * @return The first named element found
     */
    private  Node namedItem( Element topLevel, String name )
    {
        Node    node;
        Node    result;

        synchronized ( topLevel )
        {
            // Traverse all the childs of the current element in the order
	    // they appear.
            node = topLevel.getFirstChild();
            while ( node != null )
            {
                // If a particular node is an element (could be HTML or XML),
                // do two things: if it's the one we're looking for, and the
		// name (id attribute) attribute is the one we're looking for,
		// return this element; otherwise, traverse it's children.
                if ( node instanceof Element )
                {
                    if ( collectionMatch( (Element) node, name ) )
                        return node;
                    else if ( recurse() )
                    {
                        result = namedItem( (Element) node, name );
                        if ( result != null )
                            return result;
                    }
                }
                node = node.getNextSibling(); 
            }
            return node;
        }
    }
    
    
    /**
     * Returns true if scanning methods should iterate through the collection.
     * When looking for elements in the document, recursing is needed to traverse
     * the full document tree. When looking inside a specific element (e.g. for a
     * cell inside a row), recursing can lead to erroneous results.
     * 
     * @return True if methods should recurse to traverse entire tree
     */
    protected boolean recurse()
    {
        return _lookingFor > 0;
    }
    

    /**
     * Determines if current element matches based on what we're looking for.
     * The element is passed along with an optional identifier name. If the
     * element is the one we're looking for, return true. If the name is also
     * specified, the name must match the <code>id</code> attribute
     * (match <code>name</code> first for anchors).
     * 
     * @param elem The current element
     * @param name The identifier name or null
     * @return The element matches what we're looking for
     */
    protected boolean collectionMatch( Element elem, String name )
    {
        boolean    match;
        
        synchronized ( elem )
        {
            // Begin with no matching. Depending on what we're looking for,
            // attempt to match based on the element type. This is the quickest
            // way to match involving only a cast. Do the expensive string
            // comparison later on.
            match = false;
            switch ( _lookingFor )
            {
            case ANCHOR:
                // Anchor is an <A> element with a 'name' attribute. Otherwise, it's
                // just a link.
                match = ( elem instanceof HTMLAnchorElement ) &&
                        elem.getAttribute( "name" ).length() > 0;
                break;
            case FORM:
                // Any <FORM> element.
                match = ( elem instanceof HTMLFormElement );
                break;
            case IMAGE:
                // Any <IMG> element. <OBJECT> elements with images are not returned.
                match = ( elem instanceof HTMLImageElement );
                break;
            case APPLET:
                // Any <APPLET> element, and any <OBJECT> element which represents an
                // Applet. This is determined by 'codetype' attribute being
                // 'application/java' or 'classid' attribute starting with 'java:'.
                match = ( elem instanceof HTMLAppletElement ) ||
                        ( elem instanceof HTMLObjectElement &&
                          ( "application/java".equals( elem.getAttribute( "codetype" ) ) ||
                            elem.getAttribute( "classid" ).startsWith( "java:" ) ) );
                break;
            case ELEMENT:
                // All form elements implement HTMLFormControl for easy identification.
                match = ( elem instanceof HTMLFormControl );
                break;
            case LINK:
                // Any <A> element, and any <AREA> elements with an 'href' attribute.
                match = ( ( elem instanceof HTMLAnchorElement ||
                            elem instanceof HTMLAreaElement ) &&
                          elem.getAttribute( "href" ).length() > 0 );
                break;
            case AREA:
                // Any <AREA> element.
                match = ( elem instanceof HTMLAreaElement );
                break;
            case OPTION:
                // Any <OPTION> element.
                match = ( elem instanceof HTMLOptionElement );
                break;
            case ROW:
                // Any <TR> element.
                match = ( elem instanceof HTMLTableRowElement );
                break;
            case TBODY:
                // Any <TBODY> element (one of three table section types).
                match = ( elem instanceof HTMLTableSectionElement &&
                          elem.getTagName().equals( "tbody" ) );
                break;
            case CELL:
                // Any <TD> element.
                match = ( elem instanceof HTMLTableCellElement );
                break;
            }
        
            // If element type was matched and a name was specified, must also match
            // the name against either the 'id' or the 'name' attribute. The 'name'
            // attribute is relevant only for <A> elements for backward compatibility.
            if ( match && name != null )
            {
                // If an anchor and 'name' attribute matches, return true. Otherwise,
                // try 'id' attribute.
                if ( elem instanceof HTMLAnchorElement &&
                     name.equals( elem.getAttribute( "name" ) ) )
                    return true;
                match = name.equals( elem.getAttribute( "id" ) );
            }
        }
        return match;
    }

    
}


/**
 * {@link CollectionImpl#item} must traverse down the tree and decrement the
 * index until it matches an element who's index is zero. Since integers are
 * passed by value, this class servers to pass the index into each recursion
 * by reference. It encompasses all the operations that need be performed on
 * the index, although direct access is possible.
 * 
 * @see CollectionImpl#item
 */
class CollectionIndex
{
    
    
    /**
     * Returns the current index.
     * 
     * @return Current index
     */
    int getIndex()
    {
        return _index;
    }
    
    
    /**
     * Decrements the index by one.
     */
    void decrement()
    {
        -- _index;
    }
    
    
    /**
     * Returns true if index is zero (or negative).
     * 
     * @return True if index is zero
     */
    boolean isZero()
    {
        return _index <= 0;
    }
    
    
    /**
     * Constructs a new index with the specified initial value. The index will
     * then be decremeneted until it reaches zero.
     * 
     * @param index The initial value
     */
    CollectionIndex( int index )
    {
        _index = index;
    }
    
    
    /**
     * Holds the actual value that is passed by reference using this class.
     */
    private int        _index;
    

}