chore: clean up final keyword and javaDoc typo

[songkg7]

There are some changes that are not related to the functionality.

1. final keyword does not seem to be used consistently in test code.
2. final keyword is not required in the method of final class, so removed it.
3. Fixed some typos in javaDoc.

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[losalex]

Seems there is failing lint test - please take a look and fix

[songkg7]

I fixed it 😂