001: // ============================================================================
002: // $Id: Identity.java,v 1.9 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.UnaryFunctor;
036:
037: /**
038: * Unary Functor that returns the runtime argument.
039: * <p>
040: * Copyright © 2002-2005 David A. Hall
041: *
042: * @author <a href="mailto:davidahall@users.sourceforge.net">David A. Hall</a>
043: */
044:
045: public class Identity<T> extends UnaryFunctor<T, T> {
046:
047: static final long serialVersionUID = -1170897535180697025L;
048:
049: // the last value passed to fn()
050: private transient T _last;
051:
052: /**
053: * Returns the last argument that was given, or null if called prior to the
054: * first call to fn(). This value does not persist when the functor is
055: * serialized.
056: *
057: * @return the last argument that was given or null.
058: */
059: public T arg() {
060: return _last;
061: }
062:
063: // UnaryFunctor interface
064:
065: /**
066: * Given one argument, returns it.
067: *
068: * @return x
069: */
070: public T fn(T x) {
071: _last = x;
072: return x;
073: }
074:
075: /**
076: * Calls the Visitor's <code>visit(Identity)</code> method, if it
077: * implements the nested Visitor interface.
078: */
079: public void accept(net.sf.jga.fn.Visitor v) {
080: if (v instanceof Identity.Visitor)
081: ((Identity.Visitor) v).visit(this );
082: else
083: v.visit(this );
084: }
085:
086: // Object overrides
087:
088: public String toString() {
089: return "Identity";
090: }
091:
092: // AcyclicVisitor
093:
094: /**
095: * Interface for classes that may interpret an <b>Identity</b> functor.
096: */
097: public interface Visitor extends net.sf.jga.fn.Visitor {
098: public void visit(Identity host);
099: }
100: }
|