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  实现求圆形、三角形、矩形的面积和周长。要求和说明如下： (一) 定义接口sharp接口 (二) 通过实现接口定义Rect、Triangle、Circle的类，并且一个构造方法，并实现求面积和周长的方法（其中三角形斜边的计算公式c=Math.sqrt (width * width + height * height ) ） (Seeking to achieve circular, triangular, rectangular area and perimeter. Requirements and are described as follows: (a) define the interface sharp interfaces (two) by implementing the interface definition Rect, Triangle, Circle of class and a constructor method, and implement methods for the area and perimeter (where the hypotenuse of the triangle formula c = Math.sqrt (width* width+ height* height) ))