How to build a "Circle" object that lets the user determine the radius?

I'm taking an object oriented programming class and I'm having some difficulty understanding how to build a circle object that lets the user declare what the radius is.

I created a data class and in it I put my instance variable, my getter and setter methods, my constructor, and then the basic computational function methods to compute the area and perimeter of the circle with a given radius. Here is that class:

package shapesoo;
public class CircleDataClass {
private double radius;

public double getRadius() {
    return radius;
    }

public void setRadius(double radius) {
    this.radius = radius;
    }

public CircleDataClass(double radius) {
    this.radius = radius;
    }

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

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

Then, I am creating a test class that builds the circle with the given radius and in my main method I create the new circle object with:

CircleDataClass myCircle = new CircleDataClass(radius);

I don't have radius declared anywhere in this test class so that's why I am getting a run-time error. But what I want is a user to input the value for that radius parameter that I have in my constructor and then have that radius passed to this circle object. Do I create a separate method in my main class that asks for the value of the radius? I think I am getting confused with what getters/setters/cosntructors are doing and how to pass the radius variable around to different classes.

EDIT: If I put this in, is the instance variable from my data class even used?

public static void main(String[] args) {

    String shapeType = getShape();

    if (shapeType.equalsIgnoreCase("Circle")){
        String r = JOptionPane.showInputDialog("What is the radius: ");
        double radius = Double.parseDouble(r);
        CircleDataClass myCircle = new CircleDataClass(radius);

    }
}

I know how to do this without using object-oriented principles and I am aware this must seem elementary to many of you but I would appreciate any help on it.