Tuesday, 11 February 2014

Difference between == and .Equals method in C#

For Value Type
== and .Equals() method usually compare two objects by value.
int x = 10;
int y = 10;
Console.WriteLine(x == y);           // True
Console.WriteLine(x.Equals(y));      // True

For Reference Type
== performs an identity comparison, i.e. it will only return true if both references point to the same object
While Equals() method is expected to perform a value comparison, i.e. it will return true if the references point to objects that are equivalent.
StringBuilder s1 = new StringBuilder(“Yes”);
StringBuilder s2 = new StringBuilder(“Yes”);
Console.WriteLine(s1 == s2);                  // False
Console.WriteLine(s1.Equals(s2));             // True

In above example, s1 and s2 are different objects hence “==” returns false, but they are equivalent hence “Equals()” method returns true. Remember there is an exception of this rule, i.e. when you use “==” operator with string class it compares value rather than identity.

When to use “==” operator and when to use “.Equals()” method?
For value comparison, with Value Type use “==” operator, and use “Equals()” method while performing value comparison with Reference Type.

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