1/*
2 * Copyright (C) 2009 The JSR-330 Expert Group
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
17package javax.inject;
18
19/**
20 * Provides instances of {@code T}. Typically implemented by an injector. For
21 * any type {@code T} that can be injected, you can also inject
22 * {@code Provider<T>}. Compared to injecting {@code T} directly, injecting
23 * {@code Provider<T>} enables:
24 *
25 * <ul>
26 *   <li>retrieving multiple instances.</li>
27 *   <li>lazy or optional retrieval of an instance.</li>
28 *   <li>breaking circular dependencies.</li>
29 *   <li>abstracting scope so you can look up an instance in a smaller scope
30 *      from an instance in a containing scope.</li>
31 * </ul>
32 *
33 * <p>For example:
34 *
35 * <pre>
36 *   class Car {
37 *     &#064;Inject Car(Provider&lt;Seat> seatProvider) {
38 *       Seat driver = seatProvider.get();
39 *       Seat passenger = seatProvider.get();
40 *       ...
41 *     }
42 *   }</pre>
43 */
44public interface Provider<T> {
45
46    /**
47     * Provides a fully-constructed and injected instance of {@code T}.
48     *
49     * @throws RuntimeException if the injector encounters an error while
50     *  providing an instance. For example, if an injectable member on
51     *  {@code T} throws an exception, the injector may wrap the exception
52     *  and throw it to the caller of {@code get()}. Callers should not try
53     *  to handle such exceptions as the behavior may vary across injector
54     *  implementations and even different configurations of the same injector.
55     */
56    T get();
57}
58