"Will" vs. "going to" vs. Present Continious [duplicate]

Possible Duplicate:
“The train will leave” vs. “is going to leave” vs. “leaves” vs. “is leaving”

Here are three sentences:

David is going to play football next week
David is playing football next week
David will play football next week

In fact, I don't think that there is a difference between them. Am I right?

There is no denotative difference between them. Their only difference in appropriateness to a particular situation derives from tone and coherence with the audience's habits.

They are all used to describe a future event in different contexts. The choice between them depends on what has gone on previously in the conversation.