/*
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* Copyright (C) 2009 The JSR-330 Expert Group
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package javax.inject;
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import java.lang.annotation.Target;
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import java.lang.annotation.Retention;
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import java.lang.annotation.Documented;
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import static java.lang.annotation.RetentionPolicy.RUNTIME;
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import static java.lang.annotation.ElementType.ANNOTATION_TYPE;
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/**
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* Identifies scope annotations. A scope annotation applies to a class
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* containing an injectable constructor and governs how the injector reuses
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* instances of the type. By default, if no scope annotation is present, the
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* injector creates an instance (by injecting the type's constructor), uses
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* the instance for one injection, and then forgets it. If a scope annotation
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* is present, the injector may retain the instance for possible reuse in a
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* later injection. If multiple threads can access a scoped instance, its
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* implementation should be thread safe. The implementation of the scope
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* itself is left up to the injector.
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*
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* <p>In the following example, the scope annotation {@code @Singleton} ensures
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* that we only have one Log instance:
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*
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* <pre>
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* @Singleton
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* class Log {
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* void log(String message) { ... }
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* }</pre>
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*
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* <p>The injector generates an error if it encounters more than one scope
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* annotation on the same class or a scope annotation it doesn't support.
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*
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* <p>A scope annotation:
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* <ul>
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* <li>is annotated with {@code @Scope}, {@code @Retention(RUNTIME)},
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* and typically {@code @Documented}.</li>
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* <li>should not have attributes.</li>
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* <li>is typically not {@code @Inherited}, so scoping is orthogonal to
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* implementation inheritance.</li>
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* <li>may have restricted usage if annotated with {@code @Target}. While
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* this specification covers applying scopes to classes only, some
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* injector configurations might use scope annotations
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* in other places (on factory method results for example).</li>
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* </ul>
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*
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* <p>For example:
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*
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* <pre>
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* @java.lang.annotation.Documented
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* @java.lang.annotation.Retention(RUNTIME)
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* @javax.inject.Scope
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* public @interface RequestScoped {}</pre>
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*
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* <p>Annotating scope annotations with {@code @Scope} helps the injector
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* detect the case where a programmer used the scope annotation on a class but
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* forgot to configure the scope in the injector. A conservative injector
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* would generate an error rather than not apply a scope.
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*
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* @see javax.inject.Singleton @Singleton
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*/
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@Target(ANNOTATION_TYPE)
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@Retention(RUNTIME)
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@Documented
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public @interface Scope {}
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