Friday, July 13, 2007

Difference between == and .Equals Method?

What is Difference between == and .Equals() Method?

I have blogged on this topic before, but was not fully satisfied and so explaining the difference in more better way.

For Value Type: == and .Equals() method usually compare two objects by value.

For Example:

int x = 10;

int y = 10;

Console.WriteLine( x == y);

Console.WriteLine(x.Equals(y));

Will display:

True

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.

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

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 Tyep use “==” operator and use “Equals()” method while performing value comparison with Reference Type.

4 comments:

i_m_not_rude said...

If Equals for reference type evaluate objects, then
int[] arr1 = { 1 };
int[] arr2 = { 1 };
Console.WriteLine((arr1 == arr2) + “::” + (arr1.Equals(arr2)) + “::” + (ReferenceEquals(arr1, arr2)));

returns false. First and third condition return false is faitr. But why does equals also return false as they are equivalent objects. Infact is stringbuilder the only exception between == and equals, or there is some other example also?

Deepa Hoysala said...

As it is mentioned you can use it for all reference types like objects.
ex:
object obj1 = new object();
object obj2 = new object();
Console.WriteLine(obj1 == obj2);

DotNetGuts said...

Guidelines for using == and .Equal Operator in .Net

Guidelines for == and .Equal Operator

Palanivel said...

Can you explain exact difference between == and .Equals() method?

Is it correct the following points?
1. == is operator while .Equals is method.
2. == is used to the value comparison
while .Equals methods is used to compare values with reference type.

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