nullable types in c#

Question

I am a java beginner and I have to compare null values in java with null in C#.

I read that java does not assume anything to be null and always allocates memory but c# on the contrary assumes all to be null??? (did not understand what does this mean)

I also read that ordinary types in c# cannot be null but then i saw a code which says :

int? a = null;

int is ordinary type right?

I am really getting confused , can anybody help me out?

Thanks in advance

int and int? are not the same object. int? is a nullable object of type int — DotNetRussell, Feb 04 '14 at 15:52

score 3 · Answer 1 · answered Feb 04 '14 at 15:53

3

int is a primitive struct, yes. However,

int?

is syntactic sugar for

Nullable<int>

which is a completely different type.

See: http://msdn.microsoft.com/en-us/library/1t3y8s4s.aspx

answered Feb 04 '14 at 15:53

dodexahedron

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Hey.. thanks a lot... does that mean they are similar to generics in java? – user1079065 Feb 04 '14 at 15:55
1

The System.Nullable class is a generic type, meaning it can hold various other types, but the concept of generics is not equivalent to the concept of the System.Nullable class itself, no. – dodexahedron Feb 04 '14 at 15:58

score 1 · Answer 2 · answered Feb 04 '14 at 15:53

Take a look at this MSDN article:

Nullable types are instances of the System.Nullable struct. A nullable type can represent the correct range of values for its underlying value type, plus an additional null value.

class NullableExample
{
    static void Main()
    {
        int? num = null;

        // Is the HasValue property true? 
        if (num.HasValue)
        {
            System.Console.WriteLine("num = " + num.Value);
        }
        else
        {
            System.Console.WriteLine("num = Null");
        }

        // y is set to zero 
        int y = num.GetValueOrDefault();

        // num.Value throws an InvalidOperationException if num.HasValue is false 
        try
        {
            y = num.Value;
        }
        catch (System.InvalidOperationException e)
        {
            System.Console.WriteLine(e.Message);
        }
    }
}

score 0 · Answer 3 · answered Feb 04 '14 at 15:55

null is pretty similar in C# and Java. C#'s structs cannot be null, with the exception of Nullable<T> (which is itself a struct, but through some compiler magic can pretend to have a null value). Java's primitives cannot be null.

int? is shorthand for Nullable<int>. See Nullable Types for more info on that.

nullable types in c#

3 Answers3