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     */
021    package csheets.core.formula.util;
022    
023    import csheets.core.Cell;
024    import csheets.core.formula.Formula;
025    import 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     */
032    public 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    }