// java style to import library
import java.util.Scanner;
double mass;
double accel;
double Force;
double ac;
double m;

// class must alway have 1st letter as uppercase, CamelCase is Java Class convention
public class ScanPrimitives {
    public static void main(String[] args) {    
        Scanner input;

        // primitive int
        input = new Scanner(System.in);
        System.out.println("F=ma calculator");
        System.out.println("Enter the mass: ");
        try {
            double mass = input.nextDouble();
            System.out.println(mass);
            m = mass;
        } catch (Exception e) {  // if not an integer
            System.out.println("Not an integer (form like 159), " + e);
        }
        input.close();
        
        // primitive int
        input = new Scanner(System.in);
        System.out.print("Enter the accel: ");
        try {
            double accel = input.nextDouble();
            System.out.println(accel);
            ac = accel;
        } catch (Exception e) {  // if not an integer
            System.out.println("Not an integer (form like 159), " + e);
        }
        input.close();

        System.out.println("Force calculator");
        double Force = m * ac;
        System.out.print(m + "*" + ac + '=' + Force);

    

    }
    
    
}


ScanPrimitives.main(null);
F=ma calculator
Enter the mass: 
2.3
Enter the accel: 2.5
Force calculator
2.3*2.5=5.75