001    /**
002     * =========================================
003     * LibFormula : a free Java formula library
004     * =========================================
005     *
006     * Project Info:  http://reporting.pentaho.org/libformula/
007     *
008     * (C) Copyright 2006-2007, by Pentaho Corporation and Contributors.
009     *
010     * This library is free software; you can redistribute it and/or modify it under the terms
011     * of the GNU Lesser General Public License as published by the Free Software Foundation;
012     * either version 2.1 of the License, or (at your option) any later version.
013     *
014     * This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
015     * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
016     * See the GNU Lesser General Public License for more details.
017     *
018     * You should have received a copy of the GNU Lesser General Public License along with this
019     * library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
020     * Boston, MA 02111-1307, USA.
021     *
022     * [Java is a trademark or registered trademark of Sun Microsystems, Inc.
023     * in the United States and other countries.]
024     *
025     *
026     * ------------
027     * $Id: LValue.java 2716 2007-04-01 13:51:58Z taqua $
028     * ------------
029     * (C) Copyright 2006-2007, by Pentaho Corporation.
030     */
031    package org.jfree.formula.lvalues;
032    
033    import java.io.Serializable;
034    
035    import org.jfree.formula.FormulaContext;
036    import org.jfree.formula.EvaluationException;
037    import org.jfree.formula.typing.Type;
038    
039    /**
040     * A reference is an indirection to hide the details of where the actual
041     * value came from.
042     *
043     * The reference is responsible to report dependencies.
044     *
045     * @author Thomas Morgner
046     */
047    public interface LValue extends Serializable, Cloneable
048    {
049      public void initialize(FormulaContext context) throws EvaluationException;
050    
051      public TypeValuePair evaluate() throws EvaluationException;
052    
053      public Object clone() throws CloneNotSupportedException;
054    
055      /**
056       * Querying the value type is only valid *after* the value has been evaluated.
057       * @return
058       */
059      public Type getValueType();
060    
061      /**
062       * Returns any dependent lvalues (parameters and operands, mostly).
063       *
064       * @return
065       */
066      public LValue[] getChildValues();
067    
068      /**
069       * Checks, whether the LValue is constant. Constant lvalues always return
070       * the same value.
071       *
072       * @return
073       */
074      public boolean isConstant();
075    }