Introduction - If you have any usage issues, please Google them yourself
* Inheritance* properties and methods 1. subclass inherits the parent class, properties and methods of the parent class is shared by all subclasses* 2. subclass diverse subclass is polymorphic* Business case: four grid squares ( Tetromino) There are seven (I, J, L, S, Z, T, O)* implementations:* use inheritance to achieve, which is the parent class four grid squares or seven square is* a subclass is defined in the parent class Properties fourfold array subclass automatically inherits* fourfold property.* Define a four-frame box type (Tetronimo), attribute: 4 lattice method: Drop* subtype inherits the properties and methods of the class* 4 grid squares subtype each box is different, so you want to add to the subclass constructor to initialize grid position