001: // ============================================================================
002: // $Id: ConditionalGenerator.java,v 1.7 2006/01/08 00:52:25 davidahall Exp $
003: // Copyright (c) 2002-2005 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.adaptor;
034:
035: import net.sf.jga.fn.Generator;
036:
037: /**
038: * Generator that tests a condition, executes one of two given functors, and
039: * returns the result. The argument used to evaluate the condition will also
040: * be passed to whichever functor is executed. This functor implements the
041: * traditional <code><b>?:</b></code> operator.
042: * <p>
043: * Copyright © 2003-2005 David A. Hall
044: *
045: * @author <a href="mailto:davidahall@users.sourceforge.net">David A. Hall</a>
046: **/
047:
048: public class ConditionalGenerator<R> extends Generator<R> {
049:
050: static final long serialVersionUID = 5036672876367873391L;
051:
052: // The condition to be evaluated
053: private Generator<Boolean> _test;
054:
055: // The functor to execute when the condition passes
056: private Generator<R> _then;
057:
058: // The functor to execute when the condition fails
059: private Generator<R> _else;
060:
061: /**
062: * Builds a ConditionalGenerator functor, given the condition to test, and the two
063: * functors that may be executed.
064: * @throws IllegalArgumentException if any of the functors is missing
065: */
066: public ConditionalGenerator(Generator<Boolean> test,
067: Generator<R> trueFn, Generator<R> falseFn) {
068: if (test == null || trueFn == null || falseFn == null) {
069: throw new IllegalArgumentException(
070: "Three functors are required");
071: }
072:
073: _test = test;
074: _then = trueFn;
075: _else = falseFn;
076: }
077:
078: /**
079: * Returns the test functors
080: * @return the test functors
081: */
082: public Generator<Boolean> getCondition() {
083: return _test;
084: }
085:
086: /**
087: * Returns the functor that is executed when the condition is true
088: * @return the functor that is executed when the condition is true
089: */
090: public Generator<R> getTrueFunctor() {
091: return _then;
092: }
093:
094: /**
095: * Returns the functor that is executed when the condition is false
096: * @return the functor that is executed when the condition is false
097: */
098: public Generator<R> getFalseFunctor() {
099: return _else;
100: }
101:
102: // Generator interface
103:
104: /**
105: * Given argument <b>x</b>, evaluates test(x); if true, returns trueFn(x),
106: * otherwise, returns falseFn(x).
107: *
108: * @return test() ? trueFn() : falseFn()
109: */
110: public R gen() {
111: return _test.gen() ? _then.gen() : _else.gen();
112: }
113:
114: /**
115: * Calls the Visitor's <code>visit(ConditionalGenerator)</code> method, if it
116: * implements the nested Visitor interface.
117: */
118: public void accept(net.sf.jga.fn.Visitor v) {
119: if (v instanceof ConditionalGenerator.Visitor)
120: ((ConditionalGenerator.Visitor) v).visit(this );
121: else
122: v.visit(this );
123: }
124:
125: // Object overrides
126:
127: public String toString() {
128: return "ConditionalGenerator[" + _test + "?" + _then + ":"
129: + _else + "]";
130: }
131:
132: // Acyclic Visitor
133:
134: /**
135: * Interface for classes that may interpret a <b>ConditionalGenerator</b> functor.
136: */
137: public interface Visitor extends net.sf.jga.fn.Visitor {
138: public void visit(ConditionalGenerator host);
139: }
140: }
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