Accessing Databases with JDBC - Java: How to Program Early Objects

Java Reference

In-Depth Information

ResultSetTableModel Method setQuery

Method setQuery (lines 144-163) executes the query it receives as an argument to obtain

a new ResultSet (line 152). Line 155 gets the ResultSetMetaData for the new Result-

Set . Line 158 uses ResultSet method last to position the ResultSet cursor at the last

row in the ResultSet . [ Note: This can be slow if the table contains many rows.] Line 159

uses ResultSet method getRow to obtain the row number for the current row in the Re-

sultSet . Line 162 invokes method fireTableStructureChanged (inherited from class

AbstractTableModel ) to notify any JTable using this ResultSetTableModel object as its

model that the structure of the model has changed. This causes the JTable to repopulate

its rows and columns with the new ResultSet data. Method setQuery throws any excep-

tions that occur in its body back to the application that invoked setQuery .

ResultSetTableModel Method disconnectFromDatabase

Method disconnectFromDatabase (lines 166-186) implements an appropriate termina-

tion method for class ResultSetTableModel . A class designer should provide a public

method that clients of the class must invoke explicitly to free resources that an object has

used. In this case, method disconnectFromDatabase closes the ResultSet , Statement

and Connection (lines 173-175), which are considered limited resources. Clients of the

ResultSetTableModel class should always invoke this method when the instance of this

class is no longer needed. Before releasing resources, line 168 verifies whether the connec-

tion is already terminated. If not, the method proceeds. The other methods in class Re-

sultSetTableModel each throw an IllegalStateException if connectedToDatabase is

false . Method disconnectFromDatabase sets connectedToDatabase to false (line 183)

to ensure that clients do not use an instance of ResultSetTableModel after that instance

has already been terminated. IllegalStateException is an exception from the Java librar-

ies that is appropriate for indicating this error condition.

DisplayQueryResults Class

Class DisplayQueryResults (Fig. 24.28) implements the application's GUI and interacts

with the ResultSetTableModel via a JTable object. This application also demonstrates

the JTable sorting and filtering capabilities.

// Fig. 24.28: DisplayQueryResults.java

// Display the contents of the Authors table in the topics database.

import java.awt.BorderLayout;

import java.awt.event.ActionListener;

import java.awt.event.ActionEvent;

import java.awt.event.WindowAdapter;

import java.awt.event.WindowEvent;

import java.sql.SQLException;

import java.util.regex.PatternSyntaxException;

import javax.swing.JFrame;

import javax.swing.JTextArea;

import javax.swing.JScrollPane;

import javax.swing.ScrollPaneConstants;

import javax.swing.JTable;

import javax.swing.JOptionPane;

Fig. 24.28 | Display the contents of the Authors table in the books database. (Part 1 of 5.)

Java: How to Program Early Objects

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