51类的继承—子类的定义示例 Point tx: int ty int +Point +Point (int, int) +setPoint(int, int): void getxo:in +getO: int 图51 Circle -radius double +Circle(int, int, double) +setRadius (double): void +getRadiuso: double +getAreao: double +to string o: string5.1 类的继承——子类的定义示例 图5.1