Java Never Ends - Absolute Java - page 1109

This code throws three checked exceptions that must be caught: ClassNotFound
Exception, InstantiationException , and IllegalAccessException . For simplicity,
we catch only the superclass Exception in the code shown in Display 19.12.
Once the database drivers are loaded, we can connect to the database. This is done
by passing a connection string to the DriverManager.getConnection method. The
connection string specifies the protocol, database name, and other parameters, such as
whether or not a new database should be created. For example, to connect to and create
a database named BookDatabase using Derby, we would use

connection
string

Connection conn = null ;
conn = DriverManager.getConnection(
"jdbc:derby:BookDatabase; create = true");
This creates a subdirectory named BookDatabase in the active working directory that
will contain the database, files. You could specify a pathname in front of BookDatabase
if you want to create the database somewhere else on the file system. If you ever wish
to delete the database, then simply delete the BookDatabase directory. Note that if
the database already exists, then the attribute create=true will not delete the existing
database but will instead connect to the existing database.
Additional parameters are specified in the command string by separating them with
semicolons. For example, if the database requires a username and password, then the
connection string would look like this:

conn = DriverManager.getConnection
("jdbc:derby:BookDatabase;create=true;user=username;" +
"password = pass");
When we are finished accessing the database, invoke the close( ) method to close
the connection. The DriverManager.getConnection( ) method requires that
SQLException be caught, so this code should be placed inside an appropriate try/
catch block.
SQL commands or queries can be issued to JDBC once the database connection
is established. First, a Statement object must be constructed and then invoked by
calling the execute or executeQuery method with a SQL string as its argument.
The execute method can be used to execute any SQL statement, but it is generally
used for SQL commands where return values are not needed or ignored (e.g., creating
a new table or deleting a row). It returns true if the command results in a set of data
and false if there is no result or an update count. The executeQuery method is used
with a SQL query that is expected to return some rows from the database. It returns a
ResultSet object that contains the data produced by the query. These methods throw
SQLException if there is a database error. Display 19.12 illustrates how to create a
new table and insert three rows using the CREATE TABLE and INSERT commands. The
result is identical to the names table in Display 19.10. Note that the program should
only be run once. If you attempt to run it a second time, the program will throw an
exception when executing the CREATE TABLE command, because it is invalid to create
a new table that matches an existing name.