What does justice mean for characters like Atticus, Mayella, Bob, Tom and Boo in Harper Lee's To Kill a Mockingbird? Is justice served?

In Harper Lee's To Kill a Mockingbird, for Mayella Ewell, justice means nothing more than vindicating herself of her own social crime and protecting herself from her father's wrath.

As Atticus points out in his closing remarks during the trial, Mayella committed an act condemned by Maycomb's society. As Atticus phrases it, "[S]he kissed a black man. Not an old Uncle, but a strong young Negro man" (Ch. 20). Since her father saw her commit the act, she knew she had no choice but to try to clear her name, and she did so by either choosing to or going along with her father's choice to accuse Tom Robinson of rape. She also accused Robinson of rape in order to escape her father's abusiveness. As we learn from Atticus's cross-examination of the witnesses, Mayella was severely abused by "someone who led almost exclusively with his left [hand]," and Bob Ewell was the only person present who was even remotely capable of using his left hand (Ch. 20). Therefore, a second reason why Mayella accuses Robinson before the court is to escape her father's savagery, showing us that Mayella only understands justice to mean vindicating herself, meaning freeing herself of all blame and danger.

In contrast, Atticus views justice as a means of exposing the truth. Atticus pursues justice by trying to acquit Robinson of the crime he is being charged with. One of Atticus's means of acquitting Robinson is exposing the fact that since Ewell is ambidextrous and Robinson is crippled in his left arm and hand, Ewell is the more likely suspect of any wrongdoings. Yet, Atticus also knows that justice is not equally distributed to all men due to racism and prejudices. He knows that the prosecution wants the jury to believe "that all Negroes lie, that all Negroes are basically immoral beings, that all Negro men are not to be trusted around our women" (Ch. 20). As a result, he begs the jury to judge based on the actual evidence and not based on their prejudices. All in all, while Atticus knows justice can expose the truth and punish and reward those according to their deserts, he also knows that justice is only an ideal that is often hampered by men's prejudices.