001: /*
002: * Copyright 2005-2006 Sun Microsystems, Inc. All Rights Reserved.
003: * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
004: *
005: * This code is free software; you can redistribute it and/or modify it
006: * under the terms of the GNU General Public License version 2 only, as
007: * published by the Free Software Foundation. Sun designates this
008: * particular file as subject to the "Classpath" exception as provided
009: * by Sun in the LICENSE file that accompanied this code.
010: *
011: * This code is distributed in the hope that it will be useful, but WITHOUT
012: * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
013: * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
014: * version 2 for more details (a copy is included in the LICENSE file that
015: * accompanied this code).
016: *
017: * You should have received a copy of the GNU General Public License version
018: * 2 along with this work; if not, write to the Free Software Foundation,
019: * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
020: *
021: * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
022: * CA 95054 USA or visit www.sun.com if you need additional information or
023: * have any questions.
024: */
025:
026: package javax.lang.model.element;
027:
028: import javax.lang.model.util.*;
029:
030: /**
031: * A visitor of program elements, in the style of the visitor design
032: * pattern. Classes implementing this interface are used to operate
033: * on an element when the kind of element is unknown at compile time.
034: * When a visitor is passed to an element's {@link Element#accept
035: * accept} method, the <tt>visit<i>XYZ</i></tt> method most applicable
036: * to that element is invoked.
037: *
038: * <p> Classes implementing this interface may or may not throw a
039: * {@code NullPointerException} if the additional parameter {@code p}
040: * is {@code null}; see documentation of the implementing class for
041: * details.
042: *
043: * <p> <b>WARNING:</b> It is possible that methods will be added to
044: * this interface to accommodate new, currently unknown, language
045: * structures added to future versions of the Java™ programming
046: * language. Therefore, visitor classes directly implementing this
047: * interface may be source incompatible with future versions of the
048: * platform. To avoid this source incompatibility, visitor
049: * implementations are encouraged to instead extend the appropriate
050: * abstract visitor class that implements this interface. However, an
051: * API should generally use this visitor interface as the type for
052: * parameters, return type, etc. rather than one of the abstract
053: * classes.
054: *
055: * @param <R> the return type of this visitor's methods. Use {@link
056: * Void} for visitors that do not need to return results.
057: * @param <P> the type of the additional parameter to this visitor's
058: * methods. Use {@code Void} for visitors that do not need an
059: * additional parameter.
060: *
061: * @author Joseph D. Darcy
062: * @author Scott Seligman
063: * @author Peter von der Ahé
064: * @version 1.10 07/05/05
065: * @see AbstractElementVisitor6
066: * @since 1.6
067: */
068: public interface ElementVisitor<R, P> {
069: /**
070: * Visits an element.
071: * @param e the element to visit
072: * @param p a visitor-specified parameter
073: * @return a visitor-specified result
074: */
075: R visit(Element e, P p);
076:
077: /**
078: * A convenience method equivalent to {@code v.visit(e, null)}.
079: * @param e the element to visit
080: * @return a visitor-specified result
081: */
082: R visit(Element e);
083:
084: /**
085: * Visits a package element.
086: * @param e the element to visit
087: * @param p a visitor-specified parameter
088: * @return a visitor-specified result
089: */
090: R visitPackage(PackageElement e, P p);
091:
092: /**
093: * Visits a type element.
094: * @param e the element to visit
095: * @param p a visitor-specified parameter
096: * @return a visitor-specified result
097: */
098: R visitType(TypeElement e, P p);
099:
100: /**
101: * Visits a variable element.
102: * @param e the element to visit
103: * @param p a visitor-specified parameter
104: * @return a visitor-specified result
105: */
106: R visitVariable(VariableElement e, P p);
107:
108: /**
109: * Visits an executable element.
110: * @param e the element to visit
111: * @param p a visitor-specified parameter
112: * @return a visitor-specified result
113: */
114: R visitExecutable(ExecutableElement e, P p);
115:
116: /**
117: * Visits a type parameter element.
118: * @param e the element to visit
119: * @param p a visitor-specified parameter
120: * @return a visitor-specified result
121: */
122: R visitTypeParameter(TypeParameterElement e, P p);
123:
124: /**
125: * Visits an unknown kind of element.
126: * This can occur if the language evolves and new kinds
127: * of elements are added to the {@code Element} hierarchy.
128: *
129: * @param e the element to visit
130: * @param p a visitor-specified parameter
131: * @return a visitor-specified result
132: * @throws UnknownElementException
133: * a visitor implementation may optionally throw this exception
134: */
135: R visitUnknown(Element e, P p);
136: }
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