CODEWITHSUNDEEP
c#stringequality
ApceH Hypocrite
ApceH Hypocrite

Reputation: 1113

Why is Object.Equals preferred to calling String.Equals from an instance?

I am preparing for certification on C# and face the following question (code edited for simplicity):

class Class
{
    public string Name { get; set; } = "hello";
}

...

Class a = new Class();
Class b = new Class();
Class c = a;

Assert.IsTrue(a.Name == b.Name);
Assert.IsTrue(a.Name.Equals(b.Name));
Assert.IsTrue(Object.Equals(a.Name, b.Name));

Assert.IsTrue(a.Name == c.Name);
Assert.IsTrue(a.Name.Equals(c.Name));
Assert.IsTrue(Object.Equals(a.Name, c.Name));

Assert.IsTrue(a.Name == a.Name);
Assert.IsTrue(a.Name.Equals(a.Name));
Assert.IsTrue(Object.Equals(a.Name, a.Name));

All these assert passed.

Dumps of certification tests say that Object.Equals(*.Name, *.Name) is the right answer and *.Name.Equals(*.Name) is wrong.

Why?

Upvotes: 1

Views: 136

Answers (2)

Maxali
Maxali

Reputation: 1972

Object.Equals first compares object references, then it calls String.Equals for further equality check.

String.Equals tests strings for equality. It is invoked with the method name Equals or with the equality operator.

Object.Equals compares the contents of objects. It first checks whether the references are equal, as does object.ReferenceEquals. But then it calls into derived Equals methods to test equality further.

Read more explanation about Object.Equals and String.Equals

Upvotes: 1

Oleg Golovkov
Oleg Golovkov

Reputation: 706

Because x.Name.Equals(y.Name) will throw NullReferenceException if x.Name is null while Object.Equals(x.Name, y.Name) will perform a valid comparison

Upvotes: 7

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