standard interface to data that also handles inter-process communication and secure data access.
providers和provider clients提供接口用于进程间数据可靠传输和访问。
contentprovider 这是一个提供数据的接口，用户、其他进程或应用可用通过这个接口来获取数据。当然，作为创建者当然也可以对它进行增、删、改、查。
A content provider presents data to external applications as one or more tables that are similar to the tables found in a relational database.
contentprovider返回的数据是以类似于关系型数据库的表格的形式。
A row represents an instance of some type of data the provider collects, and each column in the row represents an individual piece of data collected for an instance.
some type of data the provider、an individual piece of data 一行代表许多类型的数据的集合，这一行的每一列代表该实例或者说该对象的数据单元（比如说一个学生的学号、姓名等等）
Figure 1. Relationship between content provider and other components.
Interface to global information about an application environment. This is an abstract class whose implementation is provided by the Android system. It allows access to application-specific resources and classes, as well as up-calls for application-level operations such as launching activities, broadcasting and receiving intents, etc.
全局的信息接口，抽象类，实现由android系统提供，既能依据需求访问资源以及调用函数，也能通过它接触启动程序、广播以及接收intent。
Figure 2. Overview diagram of how content providers manage access to storage.
Java中的final关键字[详解]
Java抽象类
