单例模式(Singleton) 是我们常用的一种设计模式，通常用来保证在全局情况下总是能够拿到同样的一个类实例来实现相关的工作。
单例模式很常见，因此也有戏称：

单例的写法茴香豆的茴的写法还多。

This issue might be caused by ringtone permission, if using a custom ringtone or ringtone set by other apps, must ensure your app has storage permission, otherwise, you cannot setDataUri to MediaPlayer instance.

介绍完了 Ruby 的语言基础与控制流，对于 Ruby 也算有了一个比较亲密的接触了，接下来是一些比较常用的面向对象（Object Oriented）的思想与方法。 这一部分与其它的面向对象语言比较的类似，但依然有很多地方有着鲜明的 Ruby 特色。

For example:

14.98812 -> 14.988
1.8731312 -> 1.873
2.33045 -> 2.33

In fact, this can be a n dimension hash set code sample, actually I create a 3-d hash to construct some kind of data structure for API rendering, it's not so beautiful, but easy to work, and not cost so much.

Before start, make sure that:
1. You are using macOS or Ubuntu 14.04(or higher)

1. basic system tools like git are installed. If you are using macOS, make sure you have Xcode/ Xcode Tool Chain installed.

Recently I have encountered some problems during my internship. One of our server suddenly goes very very slow, when I try to ping the server, it's always 2000-5000. After checked everything I think may cause the problem and got no answer, I decided to reboot the server.