Question

I know that it is not a good practice to call a method in the constructor of a class in C# but I stuck on something strange. My problem is that when I create an object of my class I need to assign a field in my object with a random number.

for instance

class RandomNumberHandler
    {
        private int randomNumber;
        public RandomNumberHandler()
        {
            this.randomNumber = GenerateRandomNumber();
        }

        private int GenerateRandomNumber()
        {
            return (new Random()).Next(3000) + 1000;
        }
    }

In my case I need a four digit number. I thought of generating the random number in the class where I am creating the object and passing it as a parameter to the constructor but generating a random number in the other class does not seem a very good idea either because I am trying to achieve strong cohesion for my classes. I am doing this for a “High quality code” course in my university and I am looking for the best approach. Any ideas how to do this are welcome 🙂

Answer 1

First off: there is nothing wrong with calling non-virtual methods in the constructor. Where did you read that there was? (Note: calling virtual methods can be a problem; it is not an automatic no-no, but you need to watch what you are doing very carefully).

As an aside, it seems wasteful to generate a new Random instance every time GenerateRandomNumber is called. You can extract the Random instance to a field to fix that:

class RandomNumberHandler
{
    private readonly Random random = new Random();
    private int randomNumber;

    public RandomNumberHandler()
    {
        this.randomNumber = GenerateRandomNumber();
    }

    private int GenerateRandomNumber()
    {
        return this.random.Next(3000) + 1000;
    }
}

But this raises another question: if GenerateRandomNumber is only called once in each instance’s lifetime (in the constructor), then it doesn’t make sense to create a new Random for each object. So the next logical step is to make random be static. This means that GenerateRandomNumber can also become static (and indeed, it has to):

class RandomNumberHandler
{
    private static readonly Random Random = new Random();
    private int randomNumber;

    public RandomNumberHandler()
    {
        this.randomNumber = GenerateRandomNumber();
    }

    private static int GenerateRandomNumber()
    {
        return Random.Next(3000) + 1000;
    }
}