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单例模式

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常用单例模式：

• 懒汉单例模式：

public class SingleInstance {
    public SingleInstance() {
    }
    private static  SingleInstance sInstance;
    public static SingleInstance getInstance(){
        synchronized (SingleInstance.class){//线程安全
            if (sInstance == null){
                sInstance = new SingleInstance();
            }
        }
        return sInstance;
    }
    
}

• 静态内部类单例模式：

 1 public class Singleton {  
 2     private static class SingletonHolder {  
 3     private static final Singleton INSTANCE = new Singleton();  
 4     }  
 5     private Singleton (){}
 6     public static final Singleton getInstance() {  
 7         return SingletonHolder.INSTANCE;  
 8     }  
 9 }  

Android Application 中使用单例模式：

public class MyApplication extends Application {
    private static MyApplication application;
    public static MyApplication getInstance(){
        return application;
    }
    @Override
    public void onCreate() {
        super.onCreate();
        application = this;
    }
}