After you lost data on your Samsung J2, first make sure the lost data not being overwritten by new data, if there is no backup. Then you can use Samsung data recovery software to help you recover them back. Of course, if there is a backup, you can directly recover from backup files. Usually, Samsung data recovery software like
Coolmuster Lab.Fone for Android [coolmuster.com] can help us access to the lost data and recover them back easily. About the details, you can check this article--
Samsung Galaxy Recovery: How to Recover Data from Samsung [coolmuster.com]