Getting NullReferenceException

Question

I have such a funny question.

I have the following architecture:

For example, Manager class is implemented like this:

public sealed class Manager : Interface.Abstract.Employee
{
    private Interface.IEmployee chief = null;
    private readonly Decimal bonuslimit = Convert.ToDecimal(0.4F * Convert.ToSingle(BaseSalary));

    public Manager(Person person, DateTime hiredate) 
    : base(person, hiredate)
    {
    }

    public override List<Interface.IEmployee> Subordinates
    {
        get;
        set;
    }
    public override Interface.IEmployee Chief
    {
        get
        {
            return this.chief;
        }
        set
        {
            //if(value is Associate)
            //{                    
            //    throw new SystemException("Associate can't be a chief");
            //}
            this.chief = value;
        }
    }
    public override Decimal Salary
    {
        get
        {
            var actualbonus = Convert.ToDecimal(0.01F * Convert.ToSingle(this.YearsSinceHired * BaseSalary));
            var bonus = (actualbonus > bonuslimit) ? bonuslimit : actualbonus;
            var additional = 0M;

            if(this.HasSubordinates)
            {
                foreach(Interface.Abstract.Employee employee in this.Subordinates)
                {
                    if(employee is Sales)
                    {
                        additional += employee.Salary;
                    }
                } 
            }
            return Convert.ToDecimal(Convert.ToSingle(additional) * 0.005F) + BaseSalary + bonus;
        }
    }
}

And 'factory client' that looks like this:

public class EmployeeFactoryClient
{
    private IDictionary<String, IEmployee> employees = new Dictionary<String, IEmployee>();              

    public EmployeeFactoryClient()
    { 
        this.Factory = new EmployeeFactory();            
    }
    public EmployeeFactoryClient(IEmployeeFactory factory)
    {
        this.Factory = factory;            
    }
    public IEmployeeFactory Factory { get; set; }

    public void HireEmployee(Person person, String type, String code)
    {
        this.employees.Add(
            new KeyValuePair<String, IEmployee>(
                code,
                this.Factory.Create(person, type, DateTime.Now)
            )
        );
    }
    public void DismissEmployee(String code)
    {
        this.employees.Remove(code);
    }
    public IEmployee GetEmployee(String code)
    {
        return this.employees[code];
    }
    public IEmployee this[String index]
    {
        get { return this.employees[index]; }
        private set { this.employees[index] = value; }
    }

    public Decimal TotalSalary
    {
        get
        {
            var result = 0M;
            foreach(var item in this.employees)
            {
                result += item.Value.Salary;
            }
            return result;
        }
    }        
}

And finally I have some test code:

public void SalaryTest()
    {
        #region [Persons]            
        var SalesPerson01 = new Person
        {
            Birthday = new DateTime(1980, 11, 03),
            Forename = "Corey",
            Surname = "Black",
            Gender = SexType.Female
        };
        var SalesPerson02 = new Person
        {
            Birthday = new DateTime(1980, 11, 03),
            Forename = "John",
            Surname = "Travis",
            Gender = SexType.Male
        }; 
        #endregion

        this.company.HireEmployee(SalesPerson01, "Sales", SalesPerson01.GetHashCode().ToString());
        ((Employee)this.company[SalesPerson01.GetHashCode().ToString()]).YearsSinceHired = 10;

        this.company.HireEmployee(SalesPerson02, "Sales", SalesPerson02.GetHashCode().ToString());
        ((Employee)this.company[SalesPerson02.GetHashCode().ToString()]).YearsSinceHired = 3;            

        ///////////////////////////////////////////////////////////////////
        ((Employee)this.company[SalesPerson01.GetHashCode().ToString()]).Subordinates.Add(
            this.company[SalesPerson02.GetHashCode().ToString()]
        );

        Assert.AreEqual(1405M, this.company.TotalSalary);
    }

Line ((Employee)this.company[SalesPerson01.GetHashCode().ToString()]).Subordinates.Add(this.company[SalesPerson02.GetHashCode().ToString()]); throws NullReferenceExeption. In the this.company[SalesPerson02.GetHashCode().ToString()] indexer returns IEmployee interface but not a class instance. Am I right? And if it is so how do I fix that?

Holy wall of code batman. Pare it down to something less than 1000 lines of code and I'll take a look. — RQDQ
– RQDQ, Commented Mar 15, 2011 at 20:53
Split up that line into Employee a = this.company[SalesPerson01.GetHashCode().ToString()]) etc... and see wich var is null — Stormenet
– Stormenet, Commented Mar 15, 2011 at 20:55
Does the exception indicate which member is null? My vote is that this.company is null, but it's impossible to tell. — Avilo
– Avilo, Commented Mar 15, 2011 at 20:56

Mark Byers · Accepted Answer · 2011-03-15 20:56:09Z

3

I don't see anywhere that you are initializing the Subordinates member, so I suspect that it still has the default value which is null (not the empty list). The fix is to initialize it to an empty list in the constructor:

public Manager(Person person, DateTime hiredate) : base(person, hiredate)
{
    Subordinates = new List<Interface.IEmployee>();
}

answered Mar 15, 2011 at 20:56

Mark Byers

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4 Comments

lexeme Over a year ago

Don't auto-implemented properties initialize its backing field?

Mark Byers Over a year ago

@helicera: Yes - both auto-implemented properties and plain fields are automatically initialized to the default value for the type. The problem is that the default value for reference types is null, which is obviously not what you were expecting.

RQDQ Over a year ago

@helicera - yes they do. To their default value. Which is null for reference types.

lexeme Over a year ago

Thank you very much! I didn't think about that) And sorry for the ton of code, I just couldn't formulate the problem in few words)

Robert · Accepted Answer · 2011-03-15 21:04:06Z

0

it seems you're putting in Person but then casting to Employee which are unrelated classes

answered Mar 15, 2011 at 21:04

Robert

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Comments

Vladimir Dorokhov · Accepted Answer · 2011-03-15 21:08:28Z

0

indexer returns IEmployee interface but not a class instance. Am I right?

You don't right indexer must return instance, create instance from interface impossible.

I think this.company[SalesPerson02.GetHashCode().ToString()] returns null cause you don't add SalesPerson02 instance to your company object.

answered Mar 15, 2011 at 21:08

Vladimir Dorokhov

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