定义一个类MyRectangle代表矩形，为矩形定义getwidth方法（获得矩形的宽度）。getLength方法（获得矩形的长度）SetWidth(设置宽度）getArea方法（求矩形面积）和toString方法（显示矩形格式）。为矩形派生出一个子类，MySquare代表正方形，并对getArea和toString进行重写。-Representatives to define a class MyRectangle rectangle, the rectangle defined getwidth method (to obtain the width of the rectangle). getLength method (to obtain the length of the rectangle) SetWidth (set width) getArea method (seeking rectangular area), and toString methods (the rectangle format). To derive a subclass of the rectangle, MySquare on behalf of the square, and getArea and toString rewritten.