#406 – Overriding the Equals Method

You can override the Equals method in a custom type to implement value equality for two instances of the type.

Guidelines to follow when overriding Equals include:

  • x.Equals(x) should return true
  • x.Equals(y) should return the same value as y.Equals(x)
  • x.Equals(y) and y.Equals(z) implies that x.Equals(z)
  • Repeated calls to x.Equals(y) return the same result, for the same values of x and y
  • x.Equals(null) returns false

Additionally:

  • When you override Equals, you should also override GetHashCode

Here’s the implementation of Equals for the Dog class:

        // Are two Dogs equivalent?
        public override bool Equals(object obj)
        {
            // Can't be null
            if (obj == null)
                return false;

            // Must be a Dog
            if (obj is Dog)
            {
                // Compare the dogs
                Dog d2 = (Dog)obj;
                return (Name == d2.Name) && (Age == d2.Age);
            }
            else
                return false;
        }

Here’s the override of GetHashCode.

        public override int GetHashCode()
        {
            return Name.GetHashCode() ^ Age;
        }
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About Sean
Software developer in the Twin Cities area, passionate about .NET technologies. Equally passionate about my own personal projects related to family history and preservation of family stories and photos.

2 Responses to #406 – Overriding the Equals Method

  1. JakeIL7 says:

    “When you override Equals, you should also override GetHashCode”

    Why?

    • Sean says:

      Good question. You’re anticipating tomorrow’s post, which is already written and just waiting to be published– “Why You Should Override GetHashCode When Overriding Equals”.

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