Observable.java revision e606c4d68b74293e7d7725aecbaa9c915751cd43 
1/*
2 * Copyright (C) 2014 The Android Open Source Project
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 com.android.camera.async;
18
19import com.google.common.base.Supplier;
20
21import java.util.concurrent.Executor;
22
23import javax.annotation.CheckReturnValue;
24import javax.annotation.Nonnull;
25import javax.annotation.ParametersAreNonnullByDefault;
26import javax.annotation.concurrent.ThreadSafe;
27
28/**
29 * An interface for thread-safe observable objects.
30 */
31@ThreadSafe
32@ParametersAreNonnullByDefault
33public interface Observable<T> extends Supplier<T> {
34    /**
35     * Adds the given callback to be invoked upon changes, returning a handle to
36     * be closed when the callback must be deregistered.
37     * <p>
38     * Note that the callback may be invoked multiple times even if the value
39     * has not actually changed.
40     *
41     * @param callback The callback to add.
42     * @param executor The executor on which the callback will be invoked.
43     * @return A handle to be closed when the callback must be removed.
44     */
45    @Nonnull
46    @CheckReturnValue
47    public SafeCloseable addCallback(Runnable callback, Executor executor);
48
49    /**
50     * @return The current/latest value.
51     */
52    @Nonnull
53    @Override
54    public T get();
55}
56