Joe Johnson was selected yesterday to play in the Rookie Challenge at All-Star Weekend, and Jim O'Brien is hoping it will be more than just an honor for the Celtics' top pick. He's hoping it will be a learning experience, hanging with the top players in the league.

``I don't see how it can be anything but a good thing,'' the coach said before Johnson went for six points in last night's 93-90 loss to San Antonio.

``Certainly it's an exciting time, and I believe the festivities will kind of open his eyes a little bit. And if it helps him work harder,'' O'Brien added, ``maybe he can look at all their muscles and decide that he wants to hit the weight room hard during the offseason.''