01: /**
02: * ========================================
03: * JFreeReport : a free Java report library
04: * ========================================
05: *
06: * Project Info: http://reporting.pentaho.org/
07: *
08: * (C) Copyright 2000-2007, by Object Refinery Limited, Pentaho Corporation and Contributors.
09: *
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 3048 2007-07-28 18:02:42Z tmorgner $
27: * ------------
28: * (C) Copyright 2000-2005, by Object Refinery Limited.
29: * (C) Copyright 2005-2007, by Pentaho Corporation.
30: */package org.jfree.report.expressions;
31:
32: import org.jfree.report.DataSourceException;
33:
34: /**
35: * The interface for report functions. A report function separates the business
36: * logic from presentation of the result.
37: * <p/>
38: * Since JFreeReport 0.9 functions are considered immutable. During the
39: * advancement process, the function returns a new instance with the updated
40: * state.
41: *
42: * @author Thomas Morgner
43: */
44: public interface Function extends Expression {
45: /**
46: * When the advance method is called, the function is asked to perform the
47: * next step of its computation.
48: * <p/>
49: * The original function must not be altered during that step (or more
50: * correctly, calling advance on the original expression again must not return
51: * a different result).
52: *
53: * @return a copy of the function containing the new state.
54: */
55: public Function advance() throws DataSourceException;
56: }
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