ERROR: operator does not exist: integer = character varying

Hi!

I have the following piece of jdbc code

String query = "UPDATE books SET title = ? WHERE book_id=?";
pstmt =conn.prepareStatement(query);
pstmt.setInt(1, new_book_id);
pstmt.setString(2, getStringPrompt("new title"));
pstmt.executeUpdate();

getStringPrompt returns a string and new_book_id is an int.

The structure of the books table is

books((book_id), title, author_id, subject_id)

where title is text, all the other fields are integers. author_id and
subject_id are foreign keys. When I try to run the code I get the error
message in the subject line and I can't figure out what's wrong.

regards Andreas