If you weren’t backing up your phone your Gmail account should bring your contacts back. You’d be surprised to know how much of your information actually backs up. Once the reset is complete, sign back into your Gmail account(s), Samsung account, and any other email or app accounts you may have had to recover your data. This is the most effective way to get back into your Galaxy J5.

Performing a factory reset will wipe all data from your phone. Samsung J5 Reset Password with Factory Reset