Source for org.jfree.report.expressions.Function

   1: /**
   2:  * ========================================
   3:  * JFreeReport : a free Java report library
   4:  * ========================================
   5:  *
   6:  * Project Info:  http://reporting.pentaho.org/
   7:  *
   8:  * (C) Copyright 2000-2007, by Object Refinery Limited, Pentaho Corporation and Contributors.
   9:  *
  10:  * This library is free software; you can redistribute it and/or modify it under the terms
  11:  * of the GNU Lesser General Public License as published by the Free Software Foundation;
  12:  * either version 2.1 of the License, or (at your option) any later version.
  13:  *
  14:  * This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
  15:  * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
  16:  * See the GNU Lesser General Public License for more details.
  17:  *
  18:  * You should have received a copy of the GNU Lesser General Public License along with this
  19:  * library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
  20:  * Boston, MA 02111-1307, USA.
  21:  *
  22:  * [Java is a trademark or registered trademark of Sun Microsystems, Inc.
  23:  * in the United States and other countries.]
  24:  *
  25:  * ------------
  26:  * $Id: Function.java 2725 2007-04-01 18:49:29Z taqua $
  27:  * ------------
  28:  * (C) Copyright 2000-2005, by Object Refinery Limited.
  29:  * (C) Copyright 2005-2007, by Pentaho Corporation.
  30:  */
  31: 
  32: package org.jfree.report.expressions;
  33: 
  34: import org.jfree.report.DataSourceException;
  35: 
  36: /**
  37:  * The interface for report functions.  A report function separates the business
  38:  * logic from presentation of the result.
  39:  * <p/>
  40:  * Since JFreeReport 0.9 functions are considered immutable. During the
  41:  * advancement process, the function returns a new instance with the updated
  42:  * state.
  43:  *
  44:  * @author Thomas Morgner
  45:  */
  46: public interface Function extends Expression
  47: {
  48:   /**
  49:    * When the advance method is called, the function is asked to perform the
  50:    * next step of its computation.
  51:    * <p/>
  52:    * The original function must not be altered during that step (or more
  53:    * correctly, calling advance on the original expression again must not return
  54:    * a different result).
  55:    *
  56:    * @return a copy of the function containing the new state.
  57:    */
  58:   public Function advance() throws DataSourceException;
  59: }