/*
 * Copyright (C) 2009 The JSR-330 Expert Group
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package javax.inject;

import java.lang.annotation.Target;
import java.lang.annotation.Retention;
import java.lang.annotation.Documented;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import static java.lang.annotation.ElementType.ANNOTATION_TYPE;

Identifies scope annotations. A scope annotation applies to a class
containing an injectable constructor and governs how the injector reuses
instances of the type. By default, if no scope annotation is present, the
injector creates an instance (by injecting the type's constructor), uses
the instance for one injection, and then forgets it. If a scope annotation
is present, the injector may retain the instance for possible reuse in a
later injection. If multiple threads can access a scoped instance, its
implementation should be thread safe. The implementation of the scope
itself is left up to the injector.
In the following example, the scope annotation @Singleton ensures that we only have one Log instance: 
  @Singleton
  class Log {
    void log(String message) { ... }
  }
The injector generates an error if it encounters more than one scope
annotation on the same class or a scope annotation it doesn't support.
A scope annotation:

  
is annotated with @Scope, @Retention(RUNTIME), and typically @Documented.
  
should not have attributes.
  
is typically not @Inherited, so scoping is orthogonal to implementation inheritance.
  
may have restricted usage if annotated with @Target. While this specification covers applying scopes to classes only, some injector configurations might use scope annotations in other places (on factory method results for example).

For example:
  @java.lang.annotation.Documented
  @java.lang.annotation.Retention(RUNTIME)
  @javax.inject.Scope
  public @interface RequestScoped {}
Annotating scope annotations with @Scope helps the injector detect the case where a programmer used the scope annotation on a class but forgot to configure the scope in the injector. A conservative injector would generate an error rather than not apply a scope. 
See Also:
@Singleton/**
 * Identifies scope annotations. A scope annotation applies to a class
 * containing an injectable constructor and governs how the injector reuses
 * instances of the type. By default, if no scope annotation is present, the
 * injector creates an instance (by injecting the type's constructor), uses
 * the instance for one injection, and then forgets it. If a scope annotation
 * is present, the injector may retain the instance for possible reuse in a
 * later injection. If multiple threads can access a scoped instance, its
 * implementation should be thread safe. The implementation of the scope
 * itself is left up to the injector.
 *
 * <p>In the following example, the scope annotation {@code @Singleton} ensures
 * that we only have one Log instance:
 *
 * <pre>
 *   &#064;Singleton
 *   class Log {
 *     void log(String message) { ... }
 *   }</pre>
 * 
 * <p>The injector generates an error if it encounters more than one scope
 * annotation on the same class or a scope annotation it doesn't support.
 *
 * <p>A scope annotation:
 * <ul>
 *   <li>is annotated with {@code @Scope}, {@code @Retention(RUNTIME)},
 *      and typically {@code @Documented}.</li>
 *   <li>should not have attributes.</li>
 *   <li>is typically not {@code @Inherited}, so scoping is orthogonal to
 *      implementation inheritance.</li>
 *   <li>may have restricted usage if annotated with {@code @Target}. While
 *      this specification covers applying scopes to classes only, some 
 *      injector configurations might use scope annotations
 *      in other places (on factory method results for example).</li>
 * </ul>
 *
 * <p>For example:
 *
 * <pre>
 *   &#064;java.lang.annotation.Documented
 *   &#064;java.lang.annotation.Retention(RUNTIME)
 *   &#064;javax.inject.Scope
 *   public @interface RequestScoped {}</pre>
 *
 * <p>Annotating scope annotations with {@code @Scope} helps the injector
 * detect the case where a programmer used the scope annotation on a class but
 * forgot to configure the scope in the injector. A conservative injector
 * would generate an error rather than not apply a scope.
 *
 * @see javax.inject.Singleton @Singleton
 */
@Target(ANNOTATION_TYPE)
@Retention(RUNTIME)
@Documented
public @interface Scope {}