/*

 * Copyright 2005-2006 Sun Microsystems, Inc.  All Rights Reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Sun designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Sun in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 */

package javax.lang.model.util;

import javax.lang.model.element.*;

import javax.annotation.processing.SupportedSourceVersion;

import static javax.lang.model.element.ElementKind.*;

import javax.lang.model.SourceVersion;

import static javax.lang.model.SourceVersion.*;

/**

 * A scanning visitor of program elements with default behavior

 * appropriate for the {@link SourceVersion#RELEASE_6 RELEASE_6}

 * source version.  The <tt>visit<i>XYZ</i></tt> methods in this

 * class scan their component elements by calling {@code scan} on

 * their {@linkplain Element#getEnclosedElements enclosed elements},

 * {@linkplain ExecutableElement#getParameters parameters}, etc., as

 * indicated in the individual method specifications.  A subclass can

 * control the order elements are visited by overriding the

 * <tt>visit<i>XYZ</i></tt> methods.  Note that clients of a scanner

 * may get the desired behavior be invoking {@code v.scan(e, p)} rather

 * than {@code v.visit(e, p)} on the root objects of interest.

 *

 * <p>When a subclass overrides a <tt>visit<i>XYZ</i></tt> method, the

 * new method can cause the enclosed elements to be scanned in the

 * default way by calling <tt>super.visit<i>XYZ</i></tt>.  In this

 * fashion, the concrete visitor can control the ordering of traversal

 * over the component elements with respect to the additional

 * processing; for example, consistently calling

 * <tt>super.visit<i>XYZ</i></tt> at the start of the overridden

 * methods will yield a preorder traversal, etc.  If the component

 * elements should be traversed in some other order, instead of

 * calling <tt>super.visit<i>XYZ</i></tt>, an overriding visit method

 * should call {@code scan} with the elements in the desired order.

 *

 * <p> Methods in this class may be overridden subject to their

 * general contract.  Note that annotating methods in concrete

 * subclasses with {@link java.lang.Override @Override} will help

 * ensure that methods are overridden as intended.

 *

 * <p> <b>WARNING:</b> The {@code ElementVisitor} interface

 * implemented by this class may have methods added to it in the

 * future to accommodate new, currently unknown, language structures

 * added to future versions of the Java™ programming language.

 * Therefore, methods whose names begin with {@code "visit"} may be

 * added to this class in the future; to avoid incompatibilities,

 * classes which extend this class should not declare any instance

 * methods with names beginning with {@code "visit"}.

 *

 * <p>When such a new visit method is added, the default

 * implementation in this class will be to call the {@link

 * #visitUnknown visitUnknown} method.  A new element scanner visitor

 * class will also be introduced to correspond to the new language

 * level; this visitor will have different default behavior for the

 * visit method in question.  When the new visitor is introduced, all

 * or portions of this visitor may be deprecated.

 *

 * @param <R> the return type of this visitor's methods.  Use {@link

 *            Void} for visitors that do not need to return results.

 * @param <P> the type of the additional parameter to this visitor's

 *            methods.  Use {@code Void} for visitors that do not need an

 *            additional parameter.

 *

 * @author Joseph D. Darcy

 * @author Scott Seligman

 * @author Peter von der Ahé

 * @since 1.6

 */

@SupportedSourceVersion(RELEASE_6)

public class ElementScanner6<R, P> extends AbstractElementVisitor6<R, P> {

    /**

     * The specified default value.

     */

    protected final R DEFAULT_VALUE;

    /**

     * Constructor for concrete subclasses; uses {@code null} for the

     * default value.

     */

    protected ElementScanner6(){

        DEFAULT_VALUE = null;

    }

    /**

     * Constructor for concrete subclasses; uses the argument for the

     * default value.

     */

    protected ElementScanner6(R defaultValue){

        DEFAULT_VALUE = defaultValue;

    }

    /**

     * Iterates over the given elements and calls {@link

     * #scan(Element, Object) scan(Element, P)} on each one.  Returns

     * the result of the last call to {@code scan} or {@code

     * DEFAULT_VALUE} for an empty iterable.

     *

     * @param iterable the elements to scan

     * @param  p additional parameter

     * @return the scan of the last element or {@code DEFAULT_VALUE} if no elements

     */

    public final R scan(Iterable<? extends Element> iterable, P p) {

        R result = DEFAULT_VALUE;

        for(Element e : iterable)

            result = scan(e, p);

        return result;

    }

    /**

     * Processes an element by calling {@code e.accept(this, p)};

     * this method may be overridden by subclasses.

     * @return the result of visiting {@code e}.

     */

    public R scan(Element e, P p) {

        return e.accept(this, p);

    }

    /**

     * Convenience method equivalent to {@code v.scan(e, null)}.

     * @return the result of scanning {@code e}.

     */

    public final R scan(Element e) {

        return scan(e, null);

    }

    /**

     * {@inheritDoc} This implementation scans the enclosed elements.

     *

     * @param e  the element to visit

     * @param p  a visitor-specified parameter

     * @return the result of scanning

     */

    public R visitPackage(PackageElement e, P p) {

        return scan(e.getEnclosedElements(), p);

    }

    /**

     * {@inheritDoc} This implementation scans the enclosed elements.

     *

     * @param e  the element to visit

     * @param p  a visitor-specified parameter

     * @return the result of scanning

     */

    public R visitType(TypeElement e, P p) {

        return scan(e.getEnclosedElements(), p);

    }

    /**

     * {@inheritDoc} This implementation scans the enclosed elements.

     *

     * @param e  the element to visit

     * @param p  a visitor-specified parameter

     * @return the result of scanning

     */

    public R visitVariable(VariableElement e, P p) {

        return scan(e.getEnclosedElements(), p);

    }

    /**

     * {@inheritDoc} This implementation scans the parameters.

     *

     * @param e  the element to visit

     * @param p  a visitor-specified parameter

     * @return the result of scanning

     */

    public R visitExecutable(ExecutableElement e, P p) {

        return scan(e.getParameters(), p);

    }

    /**

     * {@inheritDoc} This implementation scans the enclosed elements.

     *

     * @param e  the element to visit

     * @param p  a visitor-specified parameter

     * @return the result of scanning

     */

    public R visitTypeParameter(TypeParameterElement e, P p) {

        return scan(e.getEnclosedElements(), p);

    }

}