public sealed class FileReader
{

    private static FileReader fileReader = null;
    private static List<Entry> lines = null;
    private FileReader(string fileName)
    {
    }

    public static FileReader Instance
    {
        get
        {
            if (fileReader == null)
            {
                throw new Exception("Object not created");
            }
            return fileReader;
        }
    }

    public static void Create(string fileName)
    {
        if (fileReader != null)
        {
            throw new Exception("Object already created");
        }
        lines = new List<Entry>();
        fileReader = new FileReader(fileName);
    }
}

FileReader fr = FileReader.Instance;

FileReader fr = FileReader.Instance;
fr.Create("test.txt");