StaticClass.java revision 1551:f3b883bec2d0 
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25
26/*
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30 * file, and Oracle licenses the original version of this file under the BSD
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32 */
33/*
34   Copyright 2009-2013 Attila Szegedi
35
36   Licensed under both the Apache License, Version 2.0 (the "Apache License")
37   and the BSD License (the "BSD License"), with licensee being free to
38   choose either of the two at their discretion.
39
40   You may not use this file except in compliance with either the Apache
41   License or the BSD License.
42
43   If you choose to use this file in compliance with the Apache License, the
44   following notice applies to you:
45
46       You may obtain a copy of the Apache License at
47
48           http://www.apache.org/licenses/LICENSE-2.0
49
50       Unless required by applicable law or agreed to in writing, software
51       distributed under the License is distributed on an "AS IS" BASIS,
52       WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
53       implied. See the License for the specific language governing
54       permissions and limitations under the License.
55
56   If you choose to use this file in compliance with the BSD License, the
57   following notice applies to you:
58
59       Redistribution and use in source and binary forms, with or without
60       modification, are permitted provided that the following conditions are
61       met:
62       * Redistributions of source code must retain the above copyright
63         notice, this list of conditions and the following disclaimer.
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65         notice, this list of conditions and the following disclaimer in the
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69         this software without specific prior written permission.
70
71       THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
72       IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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76       CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
77       SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
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79       WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
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82*/
83
84package jdk.dynalink.beans;
85
86import java.io.Serializable;
87import java.util.Objects;
88import jdk.dynalink.StandardOperation;
89
90/**
91 * Object that allows access to the static members of a class (its static
92 * methods, properties, and fields), as well as construction of instances using
93 * {@link StandardOperation#NEW} operation. In Dynalink, {@link Class} objects
94 * are not treated specially and act as ordinary Java objects; you can use e.g.
95 * {@code NamedOperation(GET_PROPERTY, "superclass")} as a property getter to
96 * invoke {@code clazz.getSuperclass()}. On the other hand, you can not use
97 * {@code Class} objects to access static members of a class, nor to create new
98 * instances of the class using {@code NEW}. This is consistent with how
99 * {@code Class} objects behave in Java: in Java, you write e.g.
100 * {@code new BitSet()} instead of {@code new BitSet.class()}. Similarly, you
101 * write {@code System.out} and not {@code System.class.out}. It is this aspect
102 * of using a class name as the constructor and a namespace for static members
103 * that {@code StaticClass} embodies.
104 * <p>
105 * Objects of this class are recognized by the {@link BeansLinker} as being
106 * special, and operations on them will be linked against the represented class'
107 * static members. The {@code "class"} synthetic property is additionally
108 * recognized and returns the Java {@link Class} object, just as in Java
109 * {@code System.class} evaluates to the {@code Class} object for the
110 * {@code} System class. Conversely, {@link Class} objects exposed through
111 * {@link BeansLinker} expose the {@code "static"} synthetic property which
112 * returns their {@code StaticClass} object (there is no equivalent to this in
113 * Java).
114 * <p>
115 * In summary, instances of this class act as namespaces for static members and
116 * as constructors for classes, much the same way as specifying a class name in
117 * Java language does, except that in Java this is just a syntactic element,
118 * while in Dynalink they are expressed as actual objects.
119 * <p>{@code StaticClass} objects representing Java array types will act as
120 * constructors taking a single int argument and create an array of the
121 * specified size.
122 * <p>
123 * If the class has several constructors, {@link StandardOperation#NEW} on
124 * {@code StaticClass} will try to select the most specific applicable
125 * constructor. You might want to expose a mechanism in your language for
126 * selecting a constructor with an explicit signature through
127 * {@link BeansLinker#getConstructorMethod(Class, String)}.
128 */
129public final class StaticClass implements Serializable {
130    private static final ClassValue<StaticClass> staticClasses = new ClassValue<StaticClass>() {
131        @Override
132        protected StaticClass computeValue(final Class<?> type) {
133            return new StaticClass(type);
134        }
135    };
136
137    private static final long serialVersionUID = 1L;
138
139    /**
140     * The runtime {@code Class} object whose static members this
141     * {@code StaticClass} represents.
142     */
143    private final Class<?> clazz;
144
145    /*private*/ StaticClass(final Class<?> clazz) {
146        this.clazz = Objects.requireNonNull(clazz);
147    }
148
149    /**
150     * Retrieves the {@link StaticClass} instance for the specified class.
151     * @param clazz the class for which the static facet is requested.
152     * @return the {@link StaticClass} instance representing the specified class.
153     */
154    public static StaticClass forClass(final Class<?> clazz) {
155        return staticClasses.get(clazz);
156    }
157
158    /**
159     * Returns the represented Java class.
160     * @return the represented Java class.
161     */
162    public Class<?> getRepresentedClass() {
163        return clazz;
164    }
165
166    @Override
167    public String toString() {
168        return "StaticClass[" + clazz.getName() + "]";
169    }
170
171    /**
172     * Returns {@link #forClass(Class)} for the underlying {@code clazz} field
173     * ensuring that deserialization doesn't create non-canonical instances.
174     * @return {@link #forClass(Class)} for the underlying {@code clazz} field.
175     */
176    private Object readResolve() {
177        return forClass(clazz);
178    }
179}
180