1 /*
2  * Copyright (C) 2010 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 
17 package android.util;
18 
19 import android.compat.annotation.UnsupportedAppUsage;
20 
21 /**
22  * Singleton helper class for lazily initialization.
23  *
24  * Modeled after frameworks/base/include/utils/Singleton.h
25  *
26  * @hide
27  */
28 @android.ravenwood.annotation.RavenwoodKeepWholeClass
29 public abstract class Singleton<T> {
30 
31     @UnsupportedAppUsage
Singleton()32     public Singleton() {
33     }
34 
35     @UnsupportedAppUsage
36     private T mInstance;
37 
create()38     protected abstract T create();
39 
40     @UnsupportedAppUsage
get()41     public final T get() {
42         synchronized (this) {
43             if (mInstance == null) {
44                 mInstance = create();
45             }
46             return mInstance;
47         }
48     }
49 }
50