You can wear shorts in public, it's not a problem. I wear shorts all the time as do most male ex-pats here. Nobody gives a toss, seriously.

Swimwear is fine although Mandilular is right about Banana Hammocks. They're not actually banned here, just a crime against fashion.

Depending on what beach you go on though, you may be asked to stay in a specific area, away from the families. I mean god knows what would happen to those families if they actually saw a man with his top off. I think they melt and die or something.