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/* * @(#)ElementVisitor.java 1.4 06/07/31 * * Copyright 2006 Sun Microsystems, Inc. All rights reserved. * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */ 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>visit<i>XYZ</i></tt> 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> <b>WARNING:</b> 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. * * @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 * @version 1.4 06/07/31 * @see AbstractElementVisitor6 * @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); }