001: // ============================================================================
002: // $Id: Cast.java,v 1.6 2006/04/26 03:28:42 davidahall Exp $
003: // Copyright (c) 2004-2005 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.property;
034:
035: import java.text.MessageFormat;
036: import net.sf.jga.fn.UnaryFunctor;
037:
038: /**
039: * UnaryFunctor that returns its argument, cast to the given type. Executing
040: * the functor will throw ClassCastExceptions if the argument cannot be cast
041: * to the given type.
042: * <p>
043: * Copyright © 2004-2005 David A. Hall
044: *
045: * @author <a href="mailto:davidahall@users.sourceforge.net">David A. Hall</a>
046: **/
047:
048: public class Cast<T, R> extends UnaryFunctor<T, R> {
049:
050: static final long serialVersionUID = 2712605844695159349L;
051:
052: private Class<R> _class;
053:
054: /**
055: * Builds a Cast fuctor that returns values cast to the given type.
056: * @throws IllegalArgumentException if the method name is null or empty, or
057: * if the argument type array is null.
058: */
059: public Cast(Class<R> cl) {
060: if (cl == null)
061: throw new IllegalArgumentException("A class must be given");
062:
063: _class = cl;
064: }
065:
066: public Class<R> getCastClass() {
067: return _class;
068: }
069:
070: // UnaryPredicate interface
071:
072: public R fn(T arg) {
073: // In Java 1.5, we could write this as
074: //
075: // return _class.cast(arg);
076: //
077: // but that isn't backwards compatable with 1.4, so
078: // we'll do it another way.
079:
080: if (_class.isInstance(arg))
081: return (R) arg;
082:
083: String msg = "Cannot cast [{0}] to class {1}";
084: Object[] args = new Object[] { arg, _class.getName() };
085: ClassCastException x = new ClassCastException(MessageFormat
086: .format(msg, args));
087: throw x;
088: }
089:
090: /**
091: * Calls the Visitor's <code>visit(InstanceOf)</code> method, if it
092: * implements the nested Visitor interface.
093: */
094: public void accept(net.sf.jga.fn.Visitor v) {
095: if (v instanceof Cast.Visitor)
096: ((Cast.Visitor) v).visit(this );
097: else
098: v.visit(this );
099: }
100:
101: // Object overrides
102:
103: public String toString() {
104: return "Cast[" + _class.getName() + "]";
105: }
106:
107: // AcyclicVisitor
108:
109: /**
110: * Interface for classes that may interpret a <b>Cast</b>
111: * function.
112: */
113: public interface Visitor extends net.sf.jga.fn.Visitor {
114: public void visit(Cast host);
115: }
116: }
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