JAVA课的实验项目，题目要求是：1、定义一个接口求面积、求周长。

2、定义：圆类、矩形类、三角形类实现接口。

3、在main中以接口回调方式从键盘键入。

-JAVA class pilot project, the subject requirements are: 1, define an interface seek area, seek perimeter. 2, the definition: a round type, rectangular type, triangle class implements the interface. 3, in the main, the callback method to the interface from the keyboard.