Java example source code file (ElementVisitor.java)

This example Java source code file (ElementVisitor.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

elementvisitor

The ElementVisitor.java Java example source code

/*
 * Copyright (c) 2005, 2013, Oracle and/or its affiliates. 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.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package javax.lang.model.element;

import javax.lang.model.util.*;

/**
 * A visitor of program elements, in the style of the visitor design
 * pattern.  Classes implementing this interface are used to operate
 * on an element when the kind of element is unknown at compile time.
 * When a visitor is passed to an element's {@link Element#accept
 * accept} method, the <tt>visitXYZ method most applicable
 * to that element is invoked.
 *
 * <p> Classes implementing this interface may or may not throw a
 * {@code NullPointerException} if the additional parameter {@code p}
 * is {@code null}; see documentation of the implementing class for
 * details.
 *
 * <p> WARNING: It is possible that methods will be added to
 * this interface to accommodate new, currently unknown, language
 * structures added to future versions of the Java™ programming
 * language.  Therefore, visitor classes directly implementing this
 * interface may be source incompatible with future versions of the
 * platform.  To avoid this source incompatibility, visitor
 * implementations are encouraged to instead extend the appropriate
 * abstract visitor class that implements this interface.  However, an
 * API should generally use this visitor interface as the type for
 * parameters, return type, etc. rather than one of the abstract
 * classes.
 *
 * <p>Note that methods to accommodate new language constructs could
 * be added in a source <em>compatible way if they were added as
 * <em>default methods.  However, default methods are only
 * available on Java SE 8 and higher releases and the {@code
 * javax.lang.model.*} packages bundled in Java SE 8 are required to
 * also be runnable on Java SE 7.  Therefore, default methods
 * <em>cannot be used when extending {@code javax.lang.model.*}
 * to cover Java SE 8 language features.  However, default methods may
 * be used in subsequent revisions of the {@code javax.lang.model.*}
 * packages that are only required to run on Java SE 8 and higher
 * platform versions.
 *
 * @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
 * @see AbstractElementVisitor6
 * @see AbstractElementVisitor7
 * @since 1.6
 */
public interface ElementVisitor<R, P> {
    /**
     * Visits an element.
     * @param e  the element to visit
     * @param p  a visitor-specified parameter
     * @return a visitor-specified result
     */
    R visit(Element e, P p);

    /**
     * A convenience method equivalent to {@code v.visit(e, null)}.
     * @param e  the element to visit
     * @return a visitor-specified result
     */
    R visit(Element e);

    /**
     * Visits a package element.
     * @param e  the element to visit
     * @param p  a visitor-specified parameter
     * @return a visitor-specified result
     */
    R visitPackage(PackageElement e, P p);

    /**
     * Visits a type element.
     * @param e  the element to visit
     * @param p  a visitor-specified parameter
     * @return a visitor-specified result
     */
    R visitType(TypeElement e, P p);

    /**
     * Visits a variable element.
     * @param e  the element to visit
     * @param p  a visitor-specified parameter
     * @return a visitor-specified result
     */
    R visitVariable(VariableElement e, P p);

    /**
     * Visits an executable element.
     * @param e  the element to visit
     * @param p  a visitor-specified parameter
     * @return a visitor-specified result
     */
    R visitExecutable(ExecutableElement e, P p);

    /**
     * Visits a type parameter element.
     * @param e  the element to visit
     * @param p  a visitor-specified parameter
     * @return a visitor-specified result
     */
    R visitTypeParameter(TypeParameterElement e, P p);

    /**
     * Visits an unknown kind of element.
     * This can occur if the language evolves and new kinds
     * of elements are added to the {@code Element} hierarchy.
     *
     * @param e  the element to visit
     * @param p  a visitor-specified parameter
     * @return a visitor-specified result
     * @throws UnknownElementException
     *  a visitor implementation may optionally throw this exception
     */
    R visitUnknown(Element e, P p);
}