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C# C# Collections Sets and Dictionaries Hash Codes and Object Equality

Posted by chanjong kim
chanjong kim
2,315 Points

why?

class Department
{
    public int Id { get; set; }
    public string Name { get; set; }
}

Department dept1 = new Department() { Id = 1004, Name = "R&D" };
Department dept2 = new Department() { Id = 1004, Name = "R&D" };

dept1.Equals(dept2);

why answer is false?? Equals is not overriden, so it evaluates if dept1 is same object as dept2. both dept1 and dept2 are Department object, so I thought it returns true, But answer is false, why?

1 Answer

andren
andren
28,558 Points
andren
andren
28,558 Points

dept1 and dept2 are both objects created from the department class, but they are not the same object. The Equal method checks if two objects are the same instance of a class, not that they were built from the same class.

When the new keyword is used you create a new object from a class, which has its own state and own place in memory where it is stored. That's why you can change their properties independently of each other. In other words changing the Id of dept1 won't change the Id of dept2 and so on.

They where built from the same class, but that does not make them the same object.

If the code had been written like this:

class Department
{
    public int Id { get; set; }
    public string Name { get; set; }
}

Department dept1 = new Department() { Id = 1004, Name = "R&D" };
Department dept2 = dept1;

dept1.Equals(dept2);

Then the answer would be True as they now literally hold the same object. And changing a property in one of them would also affect the other.