New to java - class not working

[rrjava]

Hey guys, I'm extremely new to java, OOP in general, and these forums, so please bare with me. I created a circle class to use with my circle app, but for some reason its not calling the methods correctly. Im not sure if it is a problem with my app or my class. My app isnt completely done yet, but it's enough to get the program running.

Code for my App:


public class CircleApp
{

public static void main(String[] args)
{
//print to console
System.out.println("Welcome to the Circle Tester");
Scanner sc = new Scanner(System.in);
String choice = "y";


while (choice.equalsIgnoreCase("y"))

{
//get input from the user
double radius = Validator.getDouble(sc, "Enter radius: ");

Circle cir = new Circle(radius);

double circumference = cir.getCircumference();

double area = cir.getArea();

System.out.println(circumference);
System.out.println(area);

System.out.println("Would you like to continue?: y/n");
choice = sc.next();
sc.nextLine();
}
}
}

Code for class:

package Circle;


import java.util.Scanner;
import java.lang.Math;
import java.text.NumberFormat;


public class Circle
{
//the instance variables
private double radius;
private double circumference;
private double area;


//the constuctor
public Circle(double radius)
{

this.radius = radius;
circumference = 2 * Math.PI * radius;
area = Math.PI * Math.pow(radius,2);

}

//methods

public double getCircumference()
{
return circumference;
}


public String getFormattedCircumference()
{
NumberFormat number = NumberFormat.getNumberInstance();
number.setMaximumFractionDigits(2);
return number.format(this.getCircumference());
}

public double getArea()
{
return area;
}

public String getFormattedArea()
{
NumberFormat number = NumberFormat.getNumberInstance();
number.setMaximumFractionDigits(2);
return number.format(this.getArea());
}

private String formatNumber(double x)
{
NumberFormat number = NumberFormat.getNumberInstance();
number.setMaximumFractionDigits(2);
return number.format(x);
}
}

There is also a validator class, which I didn't show here. When I call the getCircumference() method, I get 0.0 as the result. Is there something wrong with where I'm coding my calculations in the class (in the constructor)? I'm a little confused about if I can code calculations in my accessor methods or not. Any help would be appreciated, thanks!

[sunde887]

Im not sure what validator is but your code looks fine, you aren't getting any errors, just incorrect results?

I copied your circle class code, added a toString method, and created a main method in the class, printing the circle, and printing the get cir and get area methods worked.

I got the following output for a circle with 10 as radius

Enter a radius: 10
Circumference 62.83185307179586, area 314.1592653589793
62.83185307179586
314.1592653589793

[rrjava]

Hmm i see, here is my code for getdouble(), I have a feeling this might be where the problem lies. I call this method in the Circle App.


public static double getDouble(Scanner sc, String prompt)
{
double d = 0;
boolean isValid = false;
while (isValid == false)
{
System.out.print(prompt);
if (sc.hasNextDouble())
{
isValid = true;
}

else
{
System.out.println("Error! Invalid decimal value. Try again.");
}
sc.nextLine(); //discard any other data entered on the line.
}
return d;
}

[sunde887]

any reason for the validator class?

You could just have the following

System.out.println("Enter number");
double area = sc.nextDouble();

In your code you never actually extract nextDouble

hasNextDouble returns boolean not a number. nextDouble returns the actual double.