继承，求矩形和圆的周长面积

package practice;import static java.lang.System.*;import java.util.*;import static java.lang.Math.*;/** * * @author Zhu Zhengyan */public class SC {    private double a;    private double b;    private double r;    public SC(double a,double b){        this.a = a;        this.b = b;    }    public SC(double r){        this.r = r;    }    public static void main(String[] args){    Scanner in = new Scanner(System.in);    out.println("please enter the length");    double a = in.nextDouble();    out.println("please enter the width");    double b = in.nextDouble();    juxing m = new juxing(a,b);    out.println("面积");    out.println(m.js(a,b));    out.println("周长");    out.println(m.jc(a,b));    out.println(m.js(a,b));    }}class juxing extends SC{    private double a;    private double b;    public juxing(double a,double b){        super(a,b);    }    public double jc(double a,double b){        return(2*a+2*b);    }    public double js(double a,double b){        return(a*b);    }}class yuan extends SC{    private double r;    public yuan(double r){        super(r);    }    public double yc(double r){        return(2*PI*r);    }    public double ys(double r){        return(PI*r*r);    }}