Wed, 23 Jan 2013 20:11:07 -0800
8006264: Add explanation of why default methods cannot be used in JDK 8 javax.lang.model
Reviewed-by: jjg
1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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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 *
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19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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24 */
26 package javax.lang.model.util;
28 import javax.lang.model.element.*;
29 import javax.annotation.processing.SupportedSourceVersion;
30 import javax.lang.model.SourceVersion;
31 import static javax.lang.model.SourceVersion.*;
33 /**
34 * A simple visitor of program elements with default behavior
35 * appropriate for the {@link SourceVersion#RELEASE_7 RELEASE_7}
36 * source version.
37 *
38 * Visit methods corresponding to {@code RELEASE_7} and earlier
39 * language constructs call {@link #defaultAction defaultAction},
40 * passing their arguments to {@code defaultAction}'s corresponding
41 * parameters.
42 *
43 * <p> Methods in this class may be overridden subject to their
44 * general contract. Note that annotating methods in concrete
45 * subclasses with {@link java.lang.Override @Override} will help
46 * ensure that methods are overridden as intended.
47 *
48 * <p> <b>WARNING:</b> The {@code ElementVisitor} interface
49 * implemented by this class may have methods added to it in the
50 * future to accommodate new, currently unknown, language structures
51 * added to future versions of the Java™ programming language.
52 * Therefore, methods whose names begin with {@code "visit"} may be
53 * added to this class in the future; to avoid incompatibilities,
54 * classes which extend this class should not declare any instance
55 * methods with names beginning with {@code "visit"}.
56 *
57 * <p>When such a new visit method is added, the default
58 * implementation in this class will be to call the {@link
59 * #visitUnknown visitUnknown} method. A new simple element visitor
60 * class will also be introduced to correspond to the new language
61 * level; this visitor will have different default behavior for the
62 * visit method in question. When the new visitor is introduced, all
63 * or portions of this visitor may be deprecated.
64 *
65 * <p>Note that adding a default implementation of a new visit method
66 * in a visitor class will occur instead of adding a <em>default
67 * method</em> directly in the visitor interface since a Java SE 8
68 * language feature cannot be used to this version of the API since
69 * this version is required to be runnable on Java SE 7
70 * implementations. Future versions of the API that are only required
71 * to run on Java SE 8 and later may take advantage of default methods
72 * in this situation.
73 *
74 * @param <R> the return type of this visitor's methods. Use {@code Void}
75 * for visitors that do not need to return results.
76 * @param <P> the type of the additional parameter to this visitor's methods. Use {@code Void}
77 * for visitors that do not need an additional parameter.
78 *
79 * @see SimpleElementVisitor6
80 * @see SimpleElementVisitor8
81 * @since 1.7
82 */
83 @SupportedSourceVersion(RELEASE_7)
84 public class SimpleElementVisitor7<R, P> extends SimpleElementVisitor6<R, P> {
85 /**
86 * Constructor for concrete subclasses; uses {@code null} for the
87 * default value.
88 */
89 protected SimpleElementVisitor7(){
90 super(null);
91 }
93 /**
94 * Constructor for concrete subclasses; uses the argument for the
95 * default value.
96 *
97 * @param defaultValue the value to assign to {@link #DEFAULT_VALUE}
98 */
99 protected SimpleElementVisitor7(R defaultValue){
100 super(defaultValue);
101 }
103 /**
104 * This implementation calls {@code defaultAction}.
105 *
106 * @param e {@inheritDoc}
107 * @param p {@inheritDoc}
108 * @return the result of {@code defaultAction}
109 */
110 @Override
111 public R visitVariable(VariableElement e, P p) {
112 return defaultAction(e, p);
113 }
114 }