001 /**
002 * ========================================
003 * JFreeReport : a free Java report library
004 * ========================================
005 *
006 * Project Info: http://reporting.pentaho.org/
007 *
008 * (C) Copyright 2000-2007, by Object Refinery Limited, 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 * $Id: Function.java,v 1.3 2007/04/01 18:49:25 taqua Exp $
027 * ------------
028 * (C) Copyright 2000-2005, by Object Refinery Limited.
029 * (C) Copyright 2005-2007, by Pentaho Corporation.
030 */
031
032 package org.jfree.report.expressions;
033
034 import org.jfree.report.DataSourceException;
035
036 /**
037 * The interface for report functions. A report function separates the business
038 * logic from presentation of the result.
039 * <p/>
040 * Since JFreeReport 0.9 functions are considered immutable. During the
041 * advancement process, the function returns a new instance with the updated
042 * state.
043 *
044 * @author Thomas Morgner
045 */
046 public interface Function extends Expression
047 {
048 /**
049 * When the advance method is called, the function is asked to perform the
050 * next step of its computation.
051 * <p/>
052 * The original function must not be altered during that step (or more
053 * correctly, calling advance on the original expression again must not return
054 * a different result).
055 *
056 * @return a copy of the function containing the new state.
057 */
058 public Function advance() throws DataSourceException;
059 }