001: // ============================================================================
002: // $Id: Average.java,v 1.3 2006/01/08 00:52:25 davidahall Exp $
003: // Copyright (c) 2005 David A. Hall
004: // ============================================================================
005: // The contents of this file are subject to the Common Development and
006: // Distribution License (CDDL), Version 1.0 (the License); you may not use this
007: // file except in compliance with the License. You should have received a copy
008: // of the the License along with this file: if not, a copy of the License is
009: // available from Sun Microsystems, Inc.
010: //
011: // http://www.sun.com/cddl/cddl.html
012: //
013: // From time to time, the license steward (initially Sun Microsystems, Inc.) may
014: // publish revised and/or new versions of the License. You may not use,
015: // distribute, or otherwise make this file available under subsequent versions
016: // of the License.
017: //
018: // Alternatively, the contents of this file may be used under the terms of the
019: // GNU Lesser General Public License Version 2.1 or later (the "LGPL"), in which
020: // case the provisions of the LGPL are applicable instead of those above. If you
021: // wish to allow use of your version of this file only under the terms of the
022: // LGPL, and not to allow others to use your version of this file under the
023: // terms of the CDDL, indicate your decision by deleting the provisions above
024: // and replace them with the notice and other provisions required by the LGPL.
025: // If you do not delete the provisions above, a recipient may use your version
026: // of this file under the terms of either the CDDL or the LGPL.
027: //
028: // This library is distributed in the hope that it will be useful,
029: // but WITHOUT ANY WARRANTY; without even the implied warranty of
030: // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
031: // ============================================================================
032:
033: package net.sf.jga.fn.arithmetic;
034:
035: import java.text.MessageFormat;
036: import java.util.Iterator;
037: import net.sf.jga.fn.UnaryFunctor;
038:
039: /**
040: * Averages numeric values in an iteration.
041: * <p>
042: * Copyright © 2005 David A. Hall
043: *
044: * @author <a href="mailto:davidahall@users.sf.net">David A. Hall</a>
045: */
046:
047: public class Average<T extends Number> extends
048: UnaryFunctor<Iterator<T>, T> {
049:
050: static final long serialVersionUID = -8341653586442484621L;
051:
052: // Utility class that performs the addition as appropriate for the
053: // class given at construction
054: private Arithmetic<T> _math;
055:
056: /**
057: * Builds a functor that averages numeric values in an iteration
058: */
059: public Average(Class<T> type) {
060: _math = ArithmeticFactory.getArithmetic(type);
061: if (_math == null) {
062: String msg = "No implementation of Arithmetic registered for {0}";
063: throw new IllegalArgumentException(MessageFormat.format(
064: msg, new Object[] { type }));
065: }
066: }
067:
068: /**
069: * Returns the average of the elements in the iteration
070: */
071: public T fn(Iterator<T> iterator) {
072: int count = 0;
073: T sum = _math.zero();
074:
075: while (iterator.hasNext()) {
076: T value = iterator.next();
077: sum = _math.plus(sum, value);
078: ++count;
079: }
080:
081: return _math.divides(sum, _math.valueOf(count));
082: }
083:
084: /**
085: * Calls the Visitor's <code>visit(Average)</code> method, if it
086: * implements the nested Visitor interface.
087: */
088: public void accept(net.sf.jga.fn.Visitor v) {
089: if (v instanceof Average.Visitor)
090: ((Average.Visitor) v).visit(this );
091: else
092: v.visit(this );
093: }
094:
095: // Object overrides
096:
097: public String toString() {
098: return "Average[]";
099: }
100:
101: // AcyclicVisitor
102:
103: /**
104: * Interface for classes that may interpret an <b>Average</b> functor.
105: */
106: public interface Visitor extends net.sf.jga.fn.Visitor {
107: public void visit(Average host);
108: }
109: }
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