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/* * @(#)TypeVisitor.java 1.5 06/07/31 * * Copyright 2006 Sun Microsystems, Inc. All rights reserved. * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */ package javax.lang.model.type; import javax.lang.model.element.*; /** * A visitor of types, in the style of the * visitor design pattern. Classes implementing this * interface are used to operate on a type when the kind of * type is unknown at compile time. When a visitor is passed to a * type's {@link TypeMirror#accept accept} method, the <tt>visit<i>XYZ</i></tt> * method most applicable to that type 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 1.5 06/07/31 * @since 1.6 */ public interface TypeVisitor<R, P> { /** * Visits a type. * @param t the type to visit * @param p a visitor-specified parameter * @return a visitor-specified result */ R visit(TypeMirror t, P p); /** * A convenience method equivalent to {@code v.visit(t, null)}. * @param t the element to visit * @return a visitor-specified result */ R visit(TypeMirror t); /** * Visits a primitive type. * @param t the type to visit * @param p a visitor-specified parameter * @return a visitor-specified result */ R visitPrimitive(PrimitiveType t, P p); /** * Visits the null type. * @param t the type to visit * @param p a visitor-specified parameter * @return a visitor-specified result */ R visitNull(NullType t, P p); /** * Visits an array type. * @param t the type to visit * @param p a visitor-specified parameter * @return a visitor-specified result */ R visitArray(ArrayType t, P p); /** * Visits a declared type. * @param t the type to visit * @param p a visitor-specified parameter * @return a visitor-specified result */ R visitDeclared(DeclaredType t, P p); /** * Visits an error type. * @param t the type to visit * @param p a visitor-specified parameter * @return a visitor-specified result */ R visitError(ErrorType t, P p); /** * Visits a type variable. * @param t the type to visit * @param p a visitor-specified parameter * @return a visitor-specified result */ R visitTypeVariable(TypeVariable t, P p); /** * Visits a wildcard type. * @param t the type to visit * @param p a visitor-specified parameter * @return a visitor-specified result */ R visitWildcard(WildcardType t, P p); /** * Visits an executable type. * @param t the type to visit * @param p a visitor-specified parameter * @return a visitor-specified result */ R visitExecutable(ExecutableType t, P p); /** * Visits a {@link NoType} instance. * @param t the type to visit * @param p a visitor-specified parameter * @return a visitor-specified result */ R visitNoType(NoType t, P p); /** * Visits an unknown kind of type. * This can occur if the language evolves and new kinds * of types are added to the {@code TypeMirror} hierarchy. * @param t the type to visit * @param p a visitor-specified parameter * @return a visitor-specified result * @throws UnknownTypeException * a visitor implementation may optionally throw this exception */ R visitUnknown(TypeMirror t, P p); }