本人初学java，哪位大佬能帮忙看看这个计算三角形面积的程序哪里错了吗？

海伦公式求三角形面积：

public class Arith {
    public void  arith(double a, double b,double c) {

        if((a + b > c)&&(a + c > b)&&(b + c > a)&&(a - b < c)&&(
                a - c < b)&&(b - c < a)) {
            double z;
              double p =(a + b + c);
             z = Math.sqrt(p * (p - a) * (p - b) * (p - c));
             System.out.print(z);
        } 
    }
}

主程序：

import java.util.*;
public class Main {
    static double a;
    static double b;
    static double c;

    public static void main(String[] args) {
        Arith brith = new Arith();
        NewScanner newscanner =new NewScanner();
        Scanner scan = new Scanner(System.in);
        System.out.println("输入三角形三边");
        if(scan.hasNextDouble()) {
        a = scan.nextDouble();
        }

        System.out.println("第二条边");
        if(scan.hasNextDouble()) {
        b = scan.nextDouble();
        }

        System.out.println("第三条边");
        if(scan.hasNextDouble()) {
        a = scan.nextDouble();
        }

        brith.arith(a, b, c);
        // TODO Auto-generated method stub

    }

}