#include, #import, what's the difference between @class?

#include and #import have the same effect, except that #import ensures that header files are imported only once, without causing duplicate imports. #import能把头文件的所有信息都获取到, contains variables and methods for this class. And @class just tells the compiler that the name that is declared later is the name of the class, and how these classes are defined is completely unknown, so even if you use @class in the header file, you need to import the header file in the Declaration file. M.

Note: @class are used in order to prevent the header files from being imported into each other (cross-import);

#include, #import, what's the difference between @class?