In the Oracle JDBC driver, there is an option to cache prepared statements. My understanding of this is that the prepared statements are precompiled by the driver, then cached, which improves performance for cached prepared statements.
My question is, does this mean that the database never has to compile those prepared statements? Does the JDBC driver send some precompiled representation, or is there still some kind of parsing/compilation that happens in the database itself?
I think that this answers your question: (sorry it is powerpoint but it defines how the prepared statement is sent to Oracle, how Oracle stores it in the Shared SQL pool, processes it, etc). The main performance gain you are getting from Prepared statements is that on the 1+nth run you are avoiding hard parses of the sql statement.
Oracle (or db of choice) will store the prepared statement, java just send's it the same statement that the db will choose from (this is limited resources however, after x time of no query the shared sql will be purged esp. of non-common queries) and then a re-parse will be required -- whether or not it is cached in your java application.