How to calculate the circumference of a circle based on the following Circle class?

Question

_{Wednesday, August 27, 2014 6:23 PM | 1 vote}

I have the following sealed Cirlce class

    public sealed class Circle
    {
        private double radius;

        public double Calculate(Func<double, double> op)
        {
            return op(radius);
        }
    }

I need to calculate the circumference of a (an arbitrary) circle based on this class without modifying the class.  Here is what I tried that is not working:

Circle cir = new Circle();
double circ = 2 * Math.PI * cir.Calculate(5, 5);

How can I calculate a circumference of a circle based on this scenario?

Rich P

All replies (6)

_{Wednesday, August 27, 2014 8:11 PM ✅Answered | 1 vote}

Ok, let's clarify:

Facts:

1. The radius-field is private, and you can't set it via a public member like a method/property.
2. You don't want to change the class, but the radius

That means in other words you want to change a private field from outside of the class, which is not nice, but possible:

Circle cir = new Circle();
var field = cir.GetType().GetField("radius",BindingFlags.Instance|BindingFlags.NonPublic);
field.SetValue(cir, 5);
double circ = cir.Calculate((radius) => 2 * Math.PI * radius);

Ha, and now, did I manage to pass the skills test question? ;-)

Thomas Claudius Huber

"If you can't make your app run faster, make it at least look & feel extremly fast"

My latest Pluralsight-course: Windows Store Apps - Data Binding in Depth

twitter: @thomasclaudiush
homepage: www.thomasclaudiushuber.com
author of: ultimate Windows Store Apps handbook | ultimate WPF handbook | ultimate Silverlight handbook

_{Wednesday, August 27, 2014 6:48 PM | 1 vote}

Hi Rich,

you can do it like this with a lambda-expression:

  Circle cir = new Circle();
  double circ = cir.Calculate((radius) => 2 * Math.PI * radius);

But note that the radius-field is 0 by default. I tried it with 5 like this:

  public sealed class Circle
    {
        private double radius = 5;

        public double Calculate(Func<double, double> op)
        {
            return op(radius);
        }
    }

I got the correct result of 31.4...

Have fun.

Thomas Claudius Huber

"If you can't make your app run faster, make it at least look & feel extremly fast"

My latest Pluralsight-course: Windows Store Apps - Data Binding in Depth

twitter: @thomasclaudiush
homepage: www.thomasclaudiushuber.com
author of: ultimate Windows Store Apps handbook | ultimate WPF handbook | ultimate Silverlight handbook

_{Wednesday, August 27, 2014 7:26 PM | 1 vote}

Thank you for your reply.  I really like the Lambda approach.  And truth be told, this was a skills test question, and I can't modify the sealed class.  In your solution you set radius = 5 inside the sealed class.   How can the 5 be used for the radius from outside of the sealed class?

Rich P

_{Wednesday, August 27, 2014 8:25 PM | 1 vote}

Thank you again.  I believe that was the whole point of the exercise -- these questions are usually always esoteric -- logical programming and efficiency not exactly the goal -- testing to see what you DO know.  This was actually a cool question (just too bad it was one of the ones I missed :).

Many thanks again.

Rich P

_{Thursday, March 12, 2015 6:23 PM | 1 vote}

Hey 

What if you're asked to use the following value

double radius = 7.5;

Then what?

_{Tuesday, April 14, 2015 4:40 PM | 2 votes}

public static class CircleExtension

{

       public static double SetRadiusAndCalculate(this Circle c, int radius)
        {
            return c.Calculate(y => { return 2 * Math.PI * radius; });
        }

}

Circle x = new Circle();
double perimeter = x.SetRadiusAndCalculate(7.5);