If my jaw hurts does it mean i have a cavity?

No. 1st, dentist.: Only thing that restrains jaw movement (generally) is the muscles that surround of connect to jaw bones. These jaw muscles (used for chewing) may be subconsciously tight/clenched. Can occur in sleep or aroused state without even realizing it. If persistent and untreated, it can lead to chronic spasm of these muscles, and chronic TMJ syndrome--which is painful and difficult to rx. Check out now.

No : There are other things besides for cavities which can cause jaw pain. See your dentist to evaluate the source of the pain.

Many reasons: to have jaw pain. Cavity, periodontal disease, infection, tumor, TMJ, referred pain from heart. See your dentist for diagnosis and treatment recommendations.