终于写出来了，参考了@新月的方法
package com.imooc.third;
public abstract class Shape {
public abstract void girth(double i, double j);
public abstract void area(double i, double j);
}package com.imooc.third;
public abstract class ShapeCircle {
public abstract void girth(double r);
public abstract void area(double r);
}package com.imooc.third;
public class Rectangle extends Shape {
@Override
public void girth(double i, double j) {
// TODO Auto-generated method stub
System.out.println("矩形的周长公式为：" + 2*(i +j));
}
@Override
public void area(double i, double j) {
// TODO Auto-generated method stub
System.out.println("矩形的面积公式为： " + i*j);
}
}package com.imooc.third;
public class Circle extends ShapeCircle {
@Override
public void girth(double r) {
// TODO Auto-generated method stub
System.out.println("圆形的周长公式为：" + 2*Math.PI*r);
}
@Override
public void area(double r) {
// TODO Auto-generated method stub
System.out.println("圆形的面积公式为：" + Math.PI*r*r);
}
}package com.imooc.third;
public class Initial {
public static void main(String[] args) {
// TODO Auto-generated method stub
Shape s1 = new Rectangle();
ShapeCircle s2 = new Circle();
s1.girth(2,3);
s1.area(2,3);
s2.girth(6);
s2.area(6);
}
}结果是：
矩形的周长公式为：10.0
矩形的面积公式为： 6.0
圆形的周长公式为：37.69911184307752
圆形的面积公式为：113.09733552923255
