Today in church I learned a better definition of joy than the other ones I've found. Joy is an expression of faith in Christ. It took me a while to realize that when the Bible mentions the mind, it is referring to our attitude. We are to have the "mind of Christ", meaning that we should have His attitude by not clinging to our rights, by humbling ourselves and serving others. What does this have to do with joy?
I think an essential difference between joy and happiness is that joy thinks long term, while happiness looks to the present. Joy looks at a long term goal, happiness demands instant gratification. Where for the joy that was set before Him Christ went to the cross, that was the ultimate long term goal. Crucifiction was the worst form of punishment for criminals in the Roman times. I heard about 6000 people being crucified by the Romans in one stretch. These people were led by Spartacus and had rebelled against the Roman empire. the emperor never allowed their bodies to be taken down. (I'm glad I didn't live during those times, I would not have the stomach for it.) Just think, for people who have sinner, for nothing that Christ did, He was nailed  to the cross and was in the most unimaginable pain. But because He endured that, we have life and hope. I think if He endured what He did, my troubles don't seem so big after that. That is the ultimate joy. Christ.
On a less serious note, I finally figures out how to make this table bigger so I'm not squinting while I'm typing this. Yay!