描述一个接口，其中含有一个求面积的方法

描述三角形类，且实现上述接口

采用继承描述直角三角形类，增加求弦长的方法，并重写求面积的方法

创建有关对象，验证程序的正确性

测试上转型对象和接口回调的有关内容

-Descr iption of an interface, which contains a descr iption of the method for the triangle area category, and the interface used to achieve the above-mentioned categories of succession of right-angled triangle described, an increase for the chord length method, and to rewrite the method for creating an area of the object, to verify the accuracy of testing procedures transformation of objects and the contents of the callback interface