I would use the following code:
s.executeUpdate("DROP TABLE IF EXISTS employee")
But depending on your verions, you could also use this:
IF OBJECT_ID('dbo.employee', 'U') IS NOT NULL
DROP TABLE dbo.employee
Answer taken from: here, also this seems like it might be a duplicate of the same post?
I would highly, highly recommend reading the SQL Documentation, and trying to do a bit more research before posting, but sense I see you are new, be sure to read the rules of posting here on StackOverFlow.