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Let's circle back to the Quidditch project.

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I ended the last Quidditch lesson by saying that for Hashmark to retrieve the key, it's not enough

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for an object to be equal to it.

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It must also share the same hash code.

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Hash map uses the hash code to find which bucket the key is in.

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And after it finds the bucket it can use equals to compare your object against the key.

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So when you add an equals method, you must always add a hash code method that assigns equal object

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to the same hash code.

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If you don't do that, you're going to get bugs.

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So here in Team Not Java, since we have an equals method, we must also add a hash code method, public

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and tache code.

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And here we can use the hash method to assign an object to hash code based on its fields'.

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In this case, house.

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Keeper seeker.

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And from experience, the hash method doesn't work with a race, so pass the string representation of

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the array, which is the same thing because equal objects are going to end up having the same Chaser's

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string.

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Ultimately, this hash method is going to assign equal object to the same hash code.

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And now I'm confident that our code should work.

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And it does work get score returns, the score for Gryffindor, the parameter we're passing in is equal

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to the key that we're interested in, which means they have the same hash code.

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We can test set score as well.

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And it works at Update's Gryffindor score to 10, the hash map was able to find a key that matches the

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hash code and a quality of the one we're passing in.

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So it knows that we're trying to update this particular key.

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So I really want to stress this.

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When you add an equals method, you must always, always add a hash code method.

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Otherwise you're going to get bugs from hash based collections.