对于各种几何图形，一般都有求图形的面积、周长等方法。现在有圆、矩形和三角形三种图形，要求通过类来实现求三种图形的面积-For a variety of geometric shapes, in general, seek graphic area, perimeter, and other methods. There are circles, rectangles and triangles three types of graphics required by the class to im