I\'d like to know what is default implementation for equality operatort (== and !=)
Is it?
public static bool operator ==(object obj1, object obj2)
{
No, it's not that - by default, references are checked for equality. Operators such as == are not polymorphic and don't call anything polymorphic by default. So for example:
string x = "Hello";
string y = new String("Hello".ToCharArray());
Console.WriteLine(x == y); // True; uses overloaded operator
object a = x;
object b = y;
Console.WriteLine(a == b); // False; uses default implementation
You can't override equality operators, but you can overload them, as string does. Whether or not you should is a different matter. I think I usually would if I were overriding Equals, but not necessarily always.