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 2725 2007-04-01 18:49:29Z taqua $ 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 }