InstanceOf.java :  » Development » jga-Generic-Algorithms » net » sf » jga » fn » property » Java Open Source

// ============================================================================
// $Id: InstanceOf.java,v 1.8 2006/04/26 03:35:01 davidahall Exp $
// Copyright (c) 2004-2005  David A. Hall
// ============================================================================
// The contents of this file are subject to the Common Development and
// Distribution License (CDDL), Version 1.0 (the License); you may not use this 
// file except in compliance with the License.  You should have received a copy
// of the the License along with this file: if not, a copy of the License is 
// available from Sun Microsystems, Inc.
//
// http://www.sun.com/cddl/cddl.html
//
// From time to time, the license steward (initially Sun Microsystems, Inc.) may
// publish revised and/or new versions of the License.  You may not use,  
// distribute, or otherwise make this file available under subsequent versions 
// of the License.
// 
// Alternatively, the contents of this file may be used under the terms of the 
// GNU Lesser General Public License Version 2.1 or later (the "LGPL"), in which
// case the provisions of the LGPL are applicable instead of those above. If you 
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// ============================================================================

package net.sf.jga.fn.property;

import net.sf.jga.fn.UnaryPredicate;

/**
 * Functor that returns true if the argument is an instance of given type.
 * <p>
 * NOTE: the generic parm T is not related to the class parameter.  If there was
 * such a relationship (ie, if the class paramater given to the constructor was
 * declared-- if it were declared Class&lt;T&gt; rather than Class&lt;?&gt;,
 * then the compiler would require that the arguemnt be of the given type to
 * compile code that uses this functor, eliminating the need for the functor
 * in the first plase.  Instead, the generic parm is the class of objects that
 * will be tested.
 * 
 * <p>
 * Copyright &copy; 2004-2005  David A. Hall
 *
 * @author <a href="mailto:davidahall@users.sourceforge.net">David A. Hall</a>
 **/

public class InstanceOf<T> extends UnaryPredicate<T> {

    static final long serialVersionUID = -1792964506358538850L;    

    private Class<?> _class;

    /**
     * Builds a InstanceOf predicate that tests against the given class.
     * @throws IllegalArgumentException if the class is null.
     */
    public InstanceOf(Class<?> cl) {
        if (cl == null)
            throw new IllegalArgumentException("A class must be given");
        
        _class = cl;
    }


    public Class<?> getTestClass() { return _class; }
    
    // UnaryPredicate interface
    
    public Boolean fn(T arg) {
        return _class.isInstance(arg);
    }

    /**
     * Calls the Visitor's <code>visit(InstanceOf)</code> method, if it
     * implements the nested Visitor interface.
     */
    public void accept(net.sf.jga.fn.Visitor v) {
        if (v instanceof InstanceOf.Visitor)
            ((InstanceOf.Visitor)v).visit(this);
        else
            v.visit(this);
    }
    
    // Object overrides

    public String toString() {
        return "InstanceOf["+_class.getName()+"]";
    }
    
   // AcyclicVisitor
    
    /**
     * Interface for classes that may interpret a <b>InstanceOf</b>
     * function.
     */
    public interface Visitor extends net.sf.jga.fn.Visitor {
        public void visit(InstanceOf host);
    }
}