Question

When using an if() statement is it better from a performance perspective to use == or !=

if(object==null)

or

if(object!=null)

Should the statement w/ the highest probability of success be first in the if() sequence?

Answer 1

I just analysed the following code in .NET Reflector:

public static void Main(string[] args)
{
    object obj2 = null;
    if (obj2 == null)
    {
        Console.WriteLine("Is null");
    }
    if (obj2 != null)
    {
        Console.WriteLine("Is not null");
    }
}

and here is the resulting IL:

.method public hidebysig static void Main(string[] args) cil managed
{
    .custom instance void [mscorlib]System.STAThreadAttribute::.ctor()
    .maxstack 1
    .locals init (
        [0] object obj2)
    L_0000: ldnull 
    L_0001: stloc.0 
    L_0002: ldloc.0 
    L_0003: brtrue.s L_000f
    L_0005: ldstr "Is null"
    L_000a: call void [mscorlib]System.Console::WriteLine(string)
    L_000f: ldloc.0 
    L_0010: brfalse.s L_001c
    L_0012: ldstr "Is not null"
    L_0017: call void [mscorlib]System.Console::WriteLine(string)
    L_001c: ret 
}

From the above it seems that it makes no difference to performance which if() check you use. But, you could look at it this way – try using the if() check which is most likely to occur. So if the object is rarely going to be null at the point of the if check, then use if(object != null).+