Scope


1   /**
2    * Copyright (C) 2006 Google Inc.
3    *
4    * Licensed under the Apache License, Version 2.0 (the "License");
5    * you may not use this file except in compliance with the License.
6    * You may obtain a copy of the License at
7    *
8    * http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS,
12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   * See the License for the specific language governing permissions and
14   * limitations under the License.
15   */
16  
17  package com.google.inject;
18  
19  /**
20   * A scope is a level of visibility that instances provided by Guice may have.
21   * By default, an instance created by the {@link Injector} has <i>no
22   * scope</i>, meaning it has no state from the framework's perspective -- the
23   * {@code Injector} creates it, injects it once into the class that required it,
24   * and then immediately forgets it. Associating a scope with a particular binding
25   * allows the created instance to be "remembered" and possibly used again for
26   * other injections.
27   *
28   * @see Scopes#SINGLETON
29   *
30   * @author crazybob@google.com (Bob Lee)
31   */
32  public interface Scope {
33  
34    /**
35     * Scopes a provider. The returned locator returns objects from this scope. If
36     * an object does not exist in this scope, the provider can use the given
37     * unscoped provider to retrieve one.
38     *
39     * <p>Scope implementations are strongly encouraged to override
40     * {@link Object#toString} in the returned provider and include the backing
41     * provider's {@code toString()} output.
42     *
43     * @param key binding key
44     * @param unscoped locates an instance when one doesn't already exist in this
45     *  scope.
46     * @return a new provider which only delegates to the given unscoped provider
47     *  when an instance of the requested object doesn't already exist in this
48     *  scope
49     */
50    public <T> Provider<T> scope(Key<T> key, Provider<T> unscoped);
51  
52    /**
53     * A short but useful description of this scope.  For comparison, the standard
54     * scopes that ship with guice use the descriptions
55     * {@code "Scopes.SINGLETON"}, {@code "ServletScopes.SESSION"} and
56     * {@code "ServletScopes.REQUEST"}.
57     */
58    String   toString();
59  }
60
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