Introduction - If you have any usage issues, please Google them yourself
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.