访问控制作用

进来学习 《Think in Java》很多Java的思想观点，深入了不少~对Access Control 的一点理解记录如下：

 

　　　Access control puts boundaries within a data type for two important reasons.The first is to establish what the client programmers can and can't use.You can build your internal mechanisms into the structure without worrying that interface that they should be using.

　　　This feeds directly into the second reason,which is to separate the interface from the implementation.If the structure is used in a set of programs,but client programmers can't do anything but send messages to the public interface,then you are free to change anything that's not public(e.g.,package access,protected,or private)without breaking client code.

　　　

　　　一开始读到，Access control 即为 implementation hidding 是不是很理解，看到这里时，忽然明白了~。implementation-实现，就是类编辑者要实现功能部分，而接口(这里的含义不是和普通类class含义相当的那个接口)就是提供给其他类调用的方法~