C# Differences between operator ==, StringBuilder.Equals, Object.Equals and Object.ReferenceEquals

Question

I have a question about Object.Equals and Equals(object). My sample code is below:

class Program
{
    static void Main(string[] args)
    {
        var sb1 = new StringBuilder("Food");
        var sb2 = new StringBuilder("Food");
        Console.WriteLine(sb1 == sb2);
        Console.WriteLine(sb1.Equals(sb2));
        Console.WriteLine(Object.Equals(sb1, sb2));
        Console.WriteLine(Object.ReferenceEquals(sb1, sb2));
        Console.ReadLine();
    }
}

The output is:

False
True
False
False

But as far as I'm concerned Object.Equals(sb1, sb2) internally calls sb1.Equals(sb2) so why does it give two different results?

Answer 1

You are missing another test:

Console.WriteLine(sb1.Equals((object)sb2)); // False!

StringBuilder does not override Equals(object), it overloads it with another Equals(StringBuilder).

Object.Equals(object, object) is calling Equals(object), so the result is false.