Using a value from a void method in another separate class.

[WeiJie Lim]

I am trying to get the area of the circle with its original radius value tripled ( using the enlargeCircle method, but is void, so I cannot invoke it in TestCircle class ) =/ .

Guidance is appreciated

public class Circle {
    double radius;
    
    public Circle(double r){
        radius = r;     //  initialising radius = 2.0
    }

    public double getRadius() {
        
        return radius;
    }
    
       public double getArea() {
        double area = Math.PI*(radius*2);
        return area;
    }
       public void enlargeCircle() {   // changes radius value by x3
          radius = radius*3;     
    }
}

public class TestCircle {
    public static void main(String[] args){

	Circle Circle1 = new Circle(2.0);
    
    double radi = Circle1.getRadius();
    double carea1 = Circle1.getArea();
    // get area of circle with original radius of 2.0
    System.out.println("Area of Circle1 with radius "+radi+" is "+carea1);
    // Now I am trying to get area of circle with its original radius tripled
}
}

[Rajdeep Biswas]

First of all, please take care of naming conventions seriously,
Circle circle1 = new Circle(2.0);

If you want to enlarge the circle, you can call enlargeCircle() method with Circle class's object reference. Then the radius increased, and you can again call getRadius() and getArea() methods to get the enlarged radius and area of the circle.
What more do you expect, please explain.

[WeiJie Lim]

Rajdeep Biswas wrote:First of all, please take care of naming conventions seriously,
Circle circle1 = new Circle(2.0);

If you want to enlarge the circle, you can call enlargeCircle() method with Circle class's object reference. Then the radius increased, and you can again call getRadius() and getArea() methods to get the enlarged radius and area of the circle.
What more do you expect, please explain.

Thanks alot. Sorry I just couldn't figure out the flow of the program just now.. I thought I have to store the return value of the void method to do it.

[fred rosenberger]

WeiJie Lim wrote:Thanks a lot. Sorry I just couldn't figure out the flow of the program just now.. I thought I have to store the return value of the void method to do it.

umm...void methods don't HAVE return values. That's what 'void' means.

[Tony Docherty]

        double area = Math.PI*(radius*2);  

Are you sure this is correct?

[WeiJie Lim]

Tony Docherty wrote:

        double area = Math.PI*(radius*2);  

Are you sure this is correct?

Oops. It should be

        double area = Math.PI*(radius*radius);  

. My bad =X.

fred rosenberger wrote:
umm...void methods don't HAVE return values. That's what 'void' means.

Yup, that's why I encountered the problem..

[Steve Myers]

The new value of radius is stored in the instance variable radius, this is a side effect of calling the enlargeCircle() method.
so

Circle1.enlargeCircle();
System.out.println("The new radius of the circle is: " + Circle1.getRadius());

as others have mentioned the variable should be called circle1 not Circle1

[Winston Gutkowski]

WeiJie Lim wrote:Guidance is appreciated

The following have nothing to do with your problem, but are just a couple of guidelines for design:

1. Try not to be redundant when naming methods.
The name enlargeCircle() is redundant, since you already know that the class is a Circle, so you really only need to call it enlarge().
Furthermore, if at some point in the future you decide to make your Circle class part of some sort of Shape hierarchy that also includes Square and Triangle, you'll be very glad that you gave your method a more generic name - enlargeCircle() doesn't make much sense for a Triangle, but enlarge() most certainly does.
Method names should generally describe an action, not a type - at least, not the type of the class that defines it.

2. When you create methods, think about flexibility.
An enlarge() method can only do one thing, but a

public void changeSize(double factor) {
   radius *= factor;
}

method allows your users to change the size any way they like.

HIH

Winston