计算圆的面积，半径不能为零和负数

package a1;

import java.util.Scanner;

public class Radius {
         public static double y(double r)throws Exception{
            double s=0;
             if(r<=0){
                throw new Exception();
            }
             s=Math.PI;
            return s;
        }

    public static void main(String[] args) throws Exception {
        Scanner sc=new Scanner(System.in);
        System.out.println("输入圆的半径：");
        int r=sc.nextInt();
        double s=0;
        try {
            s=y(r);
            System.out.println("圆的面积"+s);
        } catch (Exception e) {
            if (e instanceof Exception){
                System.out.println("参数错误");
                r=sc.nextInt();
                s=y(r);
                System.out.println("圆的面积"+s);
            }
        }
    }
}