java中方法的使用

import java.util.Scanner;
class  Demo01
{
    public static void main(String[] args) 
    {
        Scanner sc = new Scanner(System.in);
          /*System.out.println("输入");
          a = sc.nextInt();
          System.out.println("输入");
          b = sc.nextInt();
        int s = sum(a,b);
        System.out.println(s);*/
        System.out.println("输入");
        
        int c = sc.nextInt();
        double mj = mj(c);
        System.out.print(mj);
    }
    //用于求和的方法
    public static int sum(int a,int b){
          int sum = a + b;
          return sum;
    }
    //求园的面积的方法
    public static double mj(int c){
          double mj = c*c * Math.PI;
          return mj;
    }
}