Circle functions not behaving as expected in Java Class

Question

so i made a circle class that sets the radius, and should output the radius, circumference and area however, if i input the radius, the radius, circumference, area wont output back, it just shows as 0.0 heres my Circle.java

public class Circle
{
    private double radius;
    private double PI = 3.14159;

    public void setRadius(double rad)
    {
            radius = rad;
    }

    public double getRadius()
    {
            return radius;
    }

    public double getArea()
    {
            return PI * radius * radius;
    }

    public double getDiameter()
    {
            return 2 * radius;
    }

    public double getCircumference()
    {
            return 2 * PI * radius;
    }

}

and heres circledemo.java http://pastie.org/466414 -formatting didnt come out well here

First I input the radius, but when i call getRadius, circumference, area, it just outputs 0.0

Answer 1

Let's walk through the program execution, step by step. First, you initialize some variables and then create a Scanner object. Next, you enter a while loop. Inside that while loop, you display the main menu, read input from the keyboard, create a new Circle object, and then handle the input you received. And you keep doing that until flag is set to false, in which case the program exits.

Notice anything strange here?

A variable only exists inside the scope it was declared in, and your Circle object was declared inside the while loop. Remember, the body of a while loop represents one iteration of a while loop. So, essentially, your Circle object is getting re-created over and over again, which is why setRadius() is having no effect.

Answer 2

Create the Circle object instance (i.e the code Circle one = new Circle()) OUTSIDE of the while loop. Every iteration of the loop is causing the object to be re-created with new state (i.e. new radius).