import TreeVertex;

/**
 * Generic trees.
 *
 * @author Samuel A. Rebelsky
 * @author CS152 2000S
 * @version 1.0 of April 2000
 */
public interface Tree 
{

    // +------------+------------------------------------
    // | Extractors |
    // +------------+

    /**
     * Get the vertex at the root of the tree.
     * Pre: The tree is nonempty.
     * Post: Returns the vertex at the root.
     */
    public TreeVertex getRoot();

    /**
     * Determine if the tree is empty.
     * Pre: None
     * Post: Returns true if the tree is empty and false
     *       otherwise.
     */
    public boolean isEmpty();

    // +-----------+-------------------------------------
    // | Modifiers |
    // +-----------+

    /**
     * Add a vertex to the tree as a child of a particular vertex.
     * Builds a vertex for the child.
     * Pre: The vertex is in the tree.
     * Post: Added.
     * @exception Exception
     *   If the vertex limits its number of children.
     */
    public void addChild(TreeVertex parent, Object child)
        throws Exception;

    /**
     * Add a root to an empty tree.
     * Pre: The tree is empty.
     * Post: The tree contains one vertex which contains the
     *       specified value.
     */
    public void makeRoot(Object rootValue);

    /**
     * Delete a vertex from the tree.  An unpleasant operation,
     * at best.  Also deletes everything below the vertex.
     * Pre: The vertex is in the tree.
     * Post: Gone.  The parent may also have renumbered its 
     *       children.
     */
    public void delete(TreeVertex target);

} // interface Tree