JDBC Interview Questions
- What are the steps involved in establishing a JDBC connection? This action involves two steps: loading the JDBC driver and making the connection.
- How can you load the drivers?
Loading the driver or drivers you want to use is very simple and involves just one line of code. If, for example, you want to use the JDBC-ODBC Bridge driver, the following code will load it:Class.forName(”sun.jdbc.odbc.JdbcOdbcDriver”);
Your driver documentation will give you the class name to use. For instance, if the class name is jdbc.DriverXYZ, you would load the driver with the following line of code:
Class.forName(”jdbc.DriverXYZ”);
- What will Class.forName do while loading drivers? It is used to create an instance of a driver and register it with the
DriverManager. When you have loaded a driver, it is available for making a connection with a DBMS. - How can you make the connection? To establish a connection you need to have the appropriate driver connect to the DBMS.
The following line of code illustrates the general idea:String url = “jdbc:odbc:Fred”;
Connection con = DriverManager.getConnection(url, “Fernanda”, “J8?); - How can you create JDBC statements and what are they?
A Statement object is what sends your SQL statement to the DBMS. You simply create a Statement object and then execute it, supplying the appropriate execute method with the SQL statement you want to send. For a SELECT statement, the method to use is executeQuery. For statements that create or modify tables, the method to use is executeUpdate. It takes an instance of an active connection to create a Statement object. In the following example, we use our Connection object con to create the Statement objectStatement stmt = con.createStatement();
- How can you retrieve data from the ResultSet?
JDBC returns results in a ResultSet object, so we need to declare an instance of the class ResultSet to hold our results. The following code demonstrates declaring the ResultSet object rs.ResultSet rs = stmt.executeQuery(”SELECT COF_NAME, PRICE FROM COFFEES”);
String s = rs.getString(”COF_NAME”);The method getString is invoked on the ResultSet object rs, so getString() will retrieve (get) the value stored in the column COF_NAME in the current row of rs.
- What are the different types of Statements?
Regular statement (use createStatement method), prepared statement (use prepareStatement method) and callable statement (use prepareCall)
