Problem while invoking a Function from a Class

Question

I have a class that name Cleint in that i have a function ,i want to make a three instantiate from Cleint with diffrent result of a Function but the results are same here is my code:

Programm.cs:

class Program
    {
        static void Main(string[] args)
        {
            Cleint B = new Cleint();
            Cleint k = new Cleint();
            Cleint S = new Cleint();
            Console.WriteLine(B.GenerateAddress());
            Console.WriteLine(k.GenerateAddress());
            Console.WriteLine(S.GenerateAddress());
            Console.ReadLine();


        }
    }

and Cleint.cs:

class Cleint
    {
        public string GenerateAddress()
        {
            var parts = new List<string>();
            Random random = new Random();
            for (int i = 0; i < 4; i++)
            {
                int newPart = random.Next(0, 255);
                parts.Add(newPart.ToString());
            }
            string address = string.Join(".", parts);
            p;
            return address;
        }
    }

thank's for your help

possible duplicate of [Random number generator not working the way I had planned (C#)](http://stackoverflow.com/questions/767999/random-number-generator-not-working-the-way-i-had-planned-c) — Hans Passant, Sep 23 '11 at 15:22

score 2 · Answer 1 · answered Sep 23 '11 at 15:19

2

The problem is how you're using random number generation - you're creating a new instance of Random in each case.

See my article on random numbers for details, but basically you should use the same instance of Random for all the calls.

Assuming your classes aren't designed to be multithreaded, you could change it to either have a Random field in Client, or have a Random parameter in GenerateAddress. Either way, you'd create a single instance in Main and pass a reference to that same instance for all three cases.

answered Sep 23 '11 at 15:19

Jon Skeet

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Yes, this is the problem. Always instantiate as few `Random` classes as possible (always make them class-level variables). – qJake Sep 23 '11 at 15:21
2

@SpikeX: Well, while bearing in mind that they're not thread-safe... you don't want a static field. – Jon Skeet Sep 23 '11 at 15:21

score 2 · Accepted Answer · answered Sep 23 '11 at 15:20

Random is not really random - it is pseudo random and the default constructor uses the current time as the seed for the sequence.

When called in quick succession, this time will be the same and the sequence be the same.

You can use a static field to ensure you are using the same Random instance if you are only ever going to have one thread (as Random is not thread safe):

class Cleint
{
    private static Random random = new Random();

    public string GenerateAddress()
    {
        var parts = new List<string>();
        for (int i = 0; i < 4; i++)
        {
            int newPart = random.Next(0, 255);
            parts.Add(newPart.ToString());
        }
        string address = string.Join(".", parts);

        return address;
    }
}

score 1 · Answer 3 · answered Sep 23 '11 at 15:21

When you create a new Random object, it uses the current time on your PC as the seed for it's generator. If you create many Random objects in a fast succession, they'll generate the same "random" numbers.

Try creating a single Random object and generating from that.

Problem while invoking a Function from a Class

3 Answers3