001: // ============================================================================
002: // $Id: Min.java,v 1.11 2006/01/08 00:52:25 davidahall Exp $
003: // Copyright (c) 2003-2005 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: package net.sf.jga.fn.comparison;
033:
034: import java.util.Comparator;
035: import net.sf.jga.fn.BinaryFunctor;
036: import net.sf.jga.util.ComparableComparator;
037:
038: /**
039: * Binary Functor that returns the lesser of two object arguments <b>x</b>
040: * and <b>y</b>. The comparison is performed using a comparator supplied at
041: * construction time, although a default comparator will be used if the nested
042: * Comparable class' default constructor is used.
043: * The behaviour of this class in the presence of null arguments is left to the
044: * implementation of the specific Comparator, however it is generally safe to
045: * assume that using null arguments will cause a NullPointerException to be
046: * thrown.
047: * <p>
048: * To serialize a Min functor, the comparator passed at construction must be
049: * Serializable.
050: * <p>
051: * Copyright © 2003-2005 David A. Hall
052: *
053: *
054: * @author <a href="mailto:davidahall@users.sourceforge.net">David A. Hall</a>
055: **/
056:
057: public class Min<T> extends BinaryFunctor<T, T, T> {
058:
059: static final long serialVersionUID = 5803316056345309669L;
060:
061: // the comparator used to compare values
062: private Comparator/*@*/<? super T>/*@*/_comp;
063:
064: /**
065: * Builds a Less predicate using the given Comparator
066: * @throws IllegalArgumentException if the argument is null
067: */
068: public Min(Comparator<? super T> comp) {
069: if (comp == null) {
070: throw new IllegalArgumentException(
071: "Comparator may not be null");
072: }
073:
074: _comp = comp;
075: }
076:
077: /**
078: * Returns the comparator in use by this functor
079: * @return the comparator in use by this functor
080: */
081: public Comparator<? super T> getComparator() {
082: return _comp;
083: }
084:
085: // BinaryFunctor interface
086:
087: /**
088: * Returns the lesser of two arguments, or the first if they are equal.
089: * @return the lesser of two arguments, or the first if they are equal.
090: */
091: public T fn(T x, T y) {
092: return _comp.compare(x, y) <= 0 ? x : y;
093: }
094:
095: /**
096: * Calls the Visitor's <code>visit(Min)</code> method, if it
097: * implements the nested Visitor interface.
098: */
099: public void accept(net.sf.jga.fn.Visitor v) {
100: if (v instanceof Min.Visitor)
101: ((Min.Visitor) v).visit(this );
102: else
103: v.visit(this );
104: }
105:
106: // Object overrides
107:
108: public String toString() {
109: return "Min";
110: }
111:
112: // Acyclic Visitor
113:
114: /**
115: * Interface for classes that may interpret a <b>Min</b> predicate.
116: */
117: public interface Visitor extends net.sf.jga.fn.Visitor {
118: public void visit(Min host);
119: }
120:
121: /**
122: * Min functor for use with Comparable arguments. This class exists
123: * as an implementation detail that works around a limit in the javac
124: * inferencer -- in all substantive ways, this is simply a Min functor.
125: */
126:
127: static public class Comparable<T extends java.lang.Comparable/*@*/<? super T>/*@*/>
128: extends Min<T> {
129: static final long serialVersionUID = 210564993022120194L;
130:
131: public Comparable() {
132: super (new ComparableComparator<T>());
133: }
134: }
135: }
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