1 /* 2 * Copyright (c) 2005, 2011, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 package javax.lang.model.type; 27 28 import javax.lang.model.element.*; 29 30 /** 31 * A visitor of types, in the style of the 32 * visitor design pattern. Classes implementing this 33 * interface are used to operate on a type when the kind of 34 * type is unknown at compile time. When a visitor is passed to a 35 * type's {@link TypeMirror#accept accept} method, the <tt>visit<i>XYZ</i></tt> 36 * method most applicable to that type is invoked. 37 * 38 * <p> Classes implementing this interface may or may not throw a 39 * {@code NullPointerException} if the additional parameter {@code p} 40 * is {@code null}; see documentation of the implementing class for 41 * details. 42 * 43 * <p> <b>WARNING:</b> It is possible that methods will be added to 44 * this interface to accommodate new, currently unknown, language 45 * structures added to future versions of the Java™ programming 46 * language. Therefore, visitor classes directly implementing this 47 * interface may be source incompatible with future versions of the 48 * platform. To avoid this source incompatibility, visitor 49 * implementations are encouraged to instead extend the appropriate 50 * abstract visitor class that implements this interface. However, an 51 * API should generally use this visitor interface as the type for 52 * parameters, return type, etc. rather than one of the abstract 53 * classes. 54 * 55 * @param <R> the return type of this visitor's methods. Use {@link 56 * Void} for visitors that do not need to return results. 57 * @param <P> the type of the additional parameter to this visitor's 58 * methods. Use {@code Void} for visitors that do not need an 59 * additional parameter. 60 * 61 * @author Joseph D. Darcy 62 * @author Scott Seligman 63 * @author Peter von der Ahé 64 * @since 1.6 65 */ 66 public interface TypeVisitor<R, P> { 67 /** 68 * Visits a type. 69 * @param t the type to visit 70 * @param p a visitor-specified parameter 71 * @return a visitor-specified result 72 */ 73 R visit(TypeMirror t, P p); 74 75 /** 76 * A convenience method equivalent to {@code v.visit(t, null)}. 77 * @param t the element to visit 78 * @return a visitor-specified result 79 */ 80 R visit(TypeMirror t); 81 82 /** 83 * Visits a primitive type. 84 * @param t the type to visit 85 * @param p a visitor-specified parameter 86 * @return a visitor-specified result 87 */ 88 R visitPrimitive(PrimitiveType t, P p); 89 90 /** 91 * Visits the null type. 92 * @param t the type to visit 93 * @param p a visitor-specified parameter 94 * @return a visitor-specified result 95 */ 96 R visitNull(NullType t, P p); 97 98 /** 99 * Visits an array type. 100 * @param t the type to visit 101 * @param p a visitor-specified parameter 102 * @return a visitor-specified result 103 */ 104 R visitArray(ArrayType t, P p); 105 106 /** 107 * Visits a declared type. 108 * @param t the type to visit 109 * @param p a visitor-specified parameter 110 * @return a visitor-specified result 111 */ 112 R visitDeclared(DeclaredType t, P p); 113 114 /** 115 * Visits an error type. 116 * @param t the type to visit 117 * @param p a visitor-specified parameter 118 * @return a visitor-specified result 119 */ 120 R visitError(ErrorType t, P p); 121 122 /** 123 * Visits a type variable. 124 * @param t the type to visit 125 * @param p a visitor-specified parameter 126 * @return a visitor-specified result 127 */ 128 R visitTypeVariable(TypeVariable t, P p); 129 130 /** 131 * Visits a wildcard type. 132 * @param t the type to visit 133 * @param p a visitor-specified parameter 134 * @return a visitor-specified result 135 */ 136 R visitWildcard(WildcardType t, P p); 137 138 /** 139 * Visits an executable type. 140 * @param t the type to visit 141 * @param p a visitor-specified parameter 142 * @return a visitor-specified result 143 */ 144 R visitExecutable(ExecutableType t, P p); 145 146 /** 147 * Visits a {@link NoType} instance. 148 * @param t the type to visit 149 * @param p a visitor-specified parameter 150 * @return a visitor-specified result 151 */ 152 R visitNoType(NoType t, P p); 153 154 /** 155 * Visits an unknown kind of type. 156 * This can occur if the language evolves and new kinds 157 * of types are added to the {@code TypeMirror} hierarchy. 158 * @param t the type to visit 159 * @param p a visitor-specified parameter 160 * @return a visitor-specified result 161 * @throws UnknownTypeException 162 * a visitor implementation may optionally throw this exception 163 */ 164 R visitUnknown(TypeMirror t, P p); 165 166 /** 167 * Visits a disjunctive type. 168 * 169 * @param t the type to visit 170 * @param p a visitor-specified parameter 171 * @return a visitor-specified result 172 * @since 1.7 173 */ 174 R visitDisjunctive(DisjunctiveType t, P p); 175 }