单例模式

写法1:

    public SingleTaskManager(){
        
    }
    public static class SingleTaskHolder{
        private static SingleTaskManager instance = new SingleTaskManager();
    }

    public static SingleTaskManager getInstance(){
        return SingleTaskHolder.instance;
    }
}

写法2:双检查机制
synchronized加锁，加类的字节码锁，每个类能保证字节码是唯一的

public class SingleInstance2Manager {
    public static SingleInstance2Manager mInstance;
    private SingleInstance2Manager getInstance(){
        if (mInstance == null){
            synchronized (SingleInstance2Manager.class){
                if (mInstance == null){
                    mInstance = new SingleInstance2Manager();
                }
            }
        }
        return mInstance;
    }
}