为什么我们需要覆盖超类的指定初始化程序

In Aaron Hillegass' Objective-C programming book, he gives a few rules on writing custom init methods. One of the rules is that "if the designated initializer of your class is different from the designated initializer of its superclass, you must override the superclass' designated initializer so that it calls the new designated initializer (of your new class)"In Aaron Hillegass' Objective-C programming boo