Observable.java revision e919a48fb40b9d6c698a495acf40adbc0e320431 
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.android.camera.util.Callback;
20import com.google.common.base.Supplier;
21
22import java.util.concurrent.Executor;
23
24import javax.annotation.CheckReturnValue;
25import javax.annotation.Nonnull;
26import javax.annotation.ParametersAreNonnullByDefault;
27import javax.annotation.concurrent.ThreadSafe;
28
29/**
30 * An interface for thread-safe observable objects.
31 */
32@ThreadSafe
33@ParametersAreNonnullByDefault
34public interface Observable<T> extends Supplier<T> {
35    /**
36     * Adds the given callback, returning a handle to be closed when the
37     * callback must be deregistered.
38     *
39     * @param callback The callback to add.
40     * @param executor The executor on which the callback will be invoked.
41     * @return A handle to be closed when the callback must be removed.
42     */
43    @Nonnull
44    @CheckReturnValue
45    public SafeCloseable addCallback(Callback<T> callback, Executor executor);
46
47    /**
48     * @return The current/latest value.
49     */
50    @Nonnull
51    @Override
52    public T get();
53}
54