java 用接口计算圆柱的体积和面积并添加颜色

import java.util.Scanner;
class Test {
    public static void main(String[] args) {
        fangfa i = new fangfa();
        Cylinder s1 = new Cylinder();
        Cylinder s2 = new Cylinder();
        Cylinder s3 = new Cylinder();

        System.out.print("容积:");
        i.shixian(s1, 5.0, 6.0);
        System.out.print("面积:");
        i.shixian1(s2, 5.0);
        System.out.println("你想要什么颜色的容器？");
        Scanner scanner = new Scanner(System.in);
        //nextine中的L注意大写
        String str1 = scanner.nextLine();
        String color = str1;
        while (true) {
            if (str1.equals(null)) {
                System.out.println("重新输入");
                continue;
            } else {

                System.out.print("颜色:");
                //将str变量传给字符串，不需要用双引号将变量包起来
                i.shixian2(s3, str1);
                break;
            }

        }

    }
}
class Cylinder implements C{
    public double volume(double radius,double height) {
        return radius * radius * pi * height;
    }
    public double area(double radius1){
        return radius1*radius1*pi;
    }
    public String setcolor(String color){
        return color;
    }


}
class fangfa{
    public double shixian(C per,double radius,double height){
        System.out.println(per.volume(radius,height));
        return 1;

    }
    public double shixian1(C per1,double radius1){
        System.out.println(per1.area(radius1));
        return 2;
    }
    public String shixian2(C per2,String color){
        System.out.println(per2.setcolor(color));
        return "hehe";
    }
}
interface A{
    public static double pi=3.14;
     double area(double radius1);

}
interface B{
    String setcolor(String color);

}

interface C extends A,B{
    double volume(double radius,double height);

}