001/*
002 * Copyright (c) 2005 Einar Pehrson <einar@pehrson.nu>.
003 *
004 * This file is part of
005 * CleanSheets - a spreadsheet application for the Java platform.
006 *
007 * CleanSheets is free software; you can redistribute it and/or modify
008 * it under the terms of the GNU General Public License as published by
009 * the Free Software Foundation; either version 2 of the License, or
010 * (at your option) any later version.
011 *
012 * CleanSheets is distributed in the hope that it will be useful,
013 * but WITHOUT ANY WARRANTY; without even the implied warranty of
014 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
015 * GNU General Public License for more details.
016 *
017 * You should have received a copy of the GNU General Public License
018 * along with CleanSheets; if not, write to the Free Software
019 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
020 */
021package csheets.core.formula.util;
022
023import csheets.core.Cell;
024import csheets.core.formula.Formula;
025import csheets.core.formula.Reference;
026
027/**
028 * An expression visitor that looks for circular references in a formula, i.e.
029 * a reference back to the cell in the formula of a cell that precedes it.
030 * @author Einar Pehrson
031 */
032public class CircularReferenceFinder extends AbstractExpressionVisitor {
033
034        /** The cell to search for circular references */
035        private Formula formula;
036
037        /**
038         * Creates a new circular reference finder.
039         */
040        public CircularReferenceFinder() {}
041
042        /**
043         * Checks if the given formula has any circular references.
044         * @throws CircularReferenceException if the formula contains any circular references
045         */
046        public void check(Formula formula) throws CircularReferenceException {
047                this.formula = formula;
048                formula.accept(this);
049        }
050
051        /*
052         * Returns whether the given formula has any circular references.
053         * @param formula the formula to check for circularities
054         * @return true if the given formula has any circular references
055         */
056/*      public boolean hasCircularReference(Formula formula) {} */
057
058        /**
059         * Checks if the given reference causes a circular reference.
060         * @param reference the reference to visit
061         * @throws CircularReferenceException if the given reference causes a circular reference
062         */
063        public Object visitReference(Reference reference) throws CircularReferenceException, ExpressionVisitorException {
064                for (Cell precedent : reference.getCells()) {
065                        // Checks for circularity
066                        if (precedent.equals(formula.getCell()))
067                                throw new CircularReferenceException(formula);
068
069                        // Looks further
070                        Formula precedentFormula = precedent.getFormula();
071                        if (precedentFormula != null)
072                                precedentFormula.accept(this);
073                }
074                return reference;
075        }
076}