.net object equality

Question

Lets say we have two objects o1 & o2 defined as System.Object, in my situtaion o1 & o2 can be any of the following types:

• String
• Int32
• Double
• Boolean
• DateTime
• DBNull

So how can I check that o1 & o2 are equal, therefore are the same object or both have the same type & value.

Can I just do o1 == o2 or do I need to do o1.Equals(o2) or something else?

Thanks,

AJ

Answer 1

I would suggest you use

object.Equals(o1, o2)

as that will cope with nullity as well. (That assumes you want two null references to compare as equal.)

You should not use == because operators are not applied polymorphically; the types overload == but they don't override it (there's nothing to override). If you use

o1 == o2

that will compare them for reference identity, because the variables are declared to be of type object.

Using o1.Equals(o2) will work except in the case where o1 is null - at which point it would throw a NullReferenceException.

Answer 2

Operator == compare objects by reference, and method Equals compare objects by value.
For Example:

StringBuilder s1 = new StringBuilder(“Yes”);

StringBuilder s2 = new StringBuilder(“Yes”);

Console.WriteLine(s1 == s2);

Console.WriteLine(s1.Equals(s2));

Will display:

False

True

Value objects can be compared either by == or Equals.