Joy: A feeling of great pleasure and happiness. (Oxford American Dictionary)
I think those who know me would say I have joy according to this definition. I try to find pleasure in the small things, and I am generally a happy person. My little sister is always telling me I smile too much. So am I joyful? Of course!
Joy: The happy state that results from knowing and serving God. The fruit of a right relationship with God. (Holman Bible Dictionary)
This definition is quite different from the first one. Am I happy because of worldly pleasures? Do I have a happiness that is fleeting, or do I have a joy that endures because I know and am serving God? True joy, Biblical joy is the outward manifestation of the personal relationship we have with Christ. When happiness is fleeting or nonexistent it can be an indication that we are not right with God. But when we are in close fellowship with the Saviour, abiding in the center of his will, genuine joy will overflow from our hearts and lives.
The question should not be, "Am I joyful?" but rather, "How is my relationship with God?" If we focus on our relationship with Him the joy will follow.
In Your presence there is fulness of joy, in Your right hand are pleasures forevermore. -Psalm 16:11