Question

I have a function that returns an id number if the argument exists in the database. If not, it returns null. Is this begging for a null pointer exception? Negative id numbers are not permitted, but I thought it would be clearer to have non-existent arguments returning null instead of an error code like -1. What do you think?

private Integer tidOfTerm(String name) throws SQLException {
    String sql = "SELECT tid FROM term_data WHERE name = ?";
    PreparedStatement prep = conn.prepareStatement(sql);
    prep.setString(1, name);
    ResultSet result = prep.getResultSet();

    if (result.next()) {
        return result.getInt("tid");
    }

    return null; // TODO: is this begging for a null pointer exception?
}

Answer 1

This is perfectly legal. If you want to avoid a NPE, throw a custom exception. But don’t return a negative number. If the caller doesn’t check the return value, you will always have a problem. But doing false calculation (because the result is for instance multiplied by -1) is definitely harder to debug than an uncatched exception.