* 继承关系

* 1.子类继承父类的属性和方法，父类的属性和方法被所有子类共享

* 2.子类多种多样，子类是多态的

* 业务案例：四格方块（Tetromino）有七种（I,J,L,S,Z,T,O）

* 实现方式：

* 　　　　利用继承关系实现，其中四格方块是父类，七种方块是

* 　　　　子类，在父类定义四格数组的属性，子类就自动继承了

* 　　　　四格属性。

* 　　　　定义四格方块类（Tetronimo），属性：4格子，方法：下落

* 　　　　子类型继承4格方块类的属性和方法

* 子类型每个方块都不同，所以要在子类添加构造器以便以初始化格子位置-* 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-fr a me 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