Connecting to a Database
This example uses the JDBC-ODBC bridge to connect to a database called ''mydatabase''.
try {
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
String url = "jdbc:odbc:mydatabase";
Connection con = DriverManager.getConnection(
url, "login", "password");
} catch (ClassNotFoundException e) {
} catch (SQLException e) {
}
Creating a Table
This example creates a table called ''mytable'' with three columns: COL_A which holds strings, COL_B which holds integers, and COL_C which holds floating point numbers.
try {
Statement stmt = con.createStatement();
stmt.executeUpdate("CREATE TABLE mytable (
COL_A VARCHAR(100), COL_B INTEGER, COL_C FLOAT)");
} catch (SQLException e) {
}
Entering a New Row into a Table
This example enters a row containing a string, an integer, and a floating point number into the table called ''mytable''.
try {
Statement stmt = connection.createStatement();
stmt.executeUpdate("INSERT INTO mytable
VALUES ('Patrick Chan', 123, 1.23)");
connection.close();
} catch (SQLException e) {
}
Getting All Rows from a Table
This example retrieves all the rows from a table called ''mytable''. A row in ''mytable'' consists of a string, integer, and floating point number.
try {
Statement stmt = connection.createStatement();
// Get data using colunm names.
ResultSet rs = stmt.executeQuery(
"SELECT * FROM mytable");
while (rs.next()) {
String s = rs.getString("COL_A");
int i = rs.getInt("COL_B");
float f = rs.getFloat("COL_C");
process(s, i, f);
}
// Get data using colunm numbers.
rs = stmt.executeQuery(
"SELECT * FROM mytable");
while (rs.next()) {
String s = rs.getString(1);
int i = rs.getInt(2);
float f = rs.getFloat(3);
process(s, i, f);
}
} catch (SQLException e) {
}
Getting Particular Rows from a Table
This example retrieves all rows from a table called ''mytable'' whose column COL_A equals ``Patrick Chan''. A row in ''mytable'' consists of a string, integer, and floating point number.
try {
Statement stmt = connection.createStatement();
ResultSet rs = stmt.executeQuery(
"SELECT * FROM mytable WHERE COL_A = 'Patrick Chan'");
rs.next();
String s = rs.getString("COL_A");
int i = rs.getInt("COL_B");
float f = rs.getFloat("COL_C");
process(s, i, f);
} catch (SQLException e) {
}
Updating a Row of Data in a Table
This example updates a row in a table called ``mytable''. In particular, for all rows whose column COL_B equals 123, column COL_A is set to ''John Doe''.
try {
Statement stmt = connection.createStatement();
int numUpdated = stmt.executeUpdate(
"UPDATE mytable SET COL_A = 'John Doe'
WHERE COL_B = 123");
connection.close();
} catch (SQLException e) {
}
Using a Prepared Statement
A prepared statement should be used in cases where a particular SQL statement is used frequently. The prepared statement is more expensive to set up but executes faster than a statement. This example demonstrates a prepared statement for getting all rows from a table called ''mytable'' whose column COL_A equals ''Patrick Chan''. This example also demonstrates a prepared statement for updating data in the table. In particular, for all rows whose column COL_B equals 123, column COL_A is set to ''John Doe''.
try {
// Retrieving rows from the database.
PreparedStatement stmt = connection.prepareStatement(
"SELECT * FROM mytable WHERE COL_A = ?");
int colunm = 1;
stmt.setString(colunm, "Patrick Chan");
ResultSet rs = stmt.executeQuery();
// Updating the database.
stmt = connection.prepareStatement(
"UPDATE mytable SET COL_A = ? WHERE COL_B = ?");
colunm = 1;
stmt.setString(colunm, "John Doe");
colunm = 2;
stmt.setInt(colunm, 123);
int numUpdated = stmt.executeUpdate();
} catch (SQLException e) {
}
Examplets TM provided by permission of the publisher, Addision-Wesley, and Author Patrick Chan.
Handling Events with an Anonymous Class
If an event handler is specific to a component (that is, not shared by other components), there is no need to declare a class to handle the event. The event handler can be implemented using an anonymous inner class. This example demonstrates an anonymous inner class to handle key events for a component.
component.addKeyListener(new KeyAdapter() {
public void keyPressed(KeyEvent evt) {
}
});
Handling Action Events
Action events are fired by subclasses of AbstractButton and includes buttons, checkboxes, and menus.
AbstractButton button = new JButton(quot;OK");
button.addActionListener(new MyActionListener());
public class MyActionListener
implements ActionListener {
public void actionPerformed(ActionEvent evt) {
// Determine which abstract
// button fired the event.
AbstractButton button =
(AbstractButton)evt.getSource();
}
}
Handling Key Presses
You can get the key that was pressed either as a key character (which is a Unicode character) or as a key code (a special value representing a particular key on the keyboard).
component.addKeyListener(new MyKeyListener());
public class MyKeyListener extends KeyAdapter {
public void keyPressed(KeyEvent evt) {
// Check for key characters.
if (evt.getKeyChar() == 'a') {
process(evt.getKeyChar());
}
// Check for key codes.
if (evt.getKeyCode() == KeyEvent.VK_HOME) {
process(evt.getKeyCode());
}
}
}
Handling Mouse Clicks
component.addMouseListener(
new MyMouseListener());
public class MyMouseListener
extends MouseAdapter {
public void mouseClicked(MouseEvent evt) {
if ((evt.getModifiers() &
InputEvent.BUTTON1_MASK) != 0) {
processLeft(evt.getPoint());
}
if ((evt.getModifiers() &
InputEvent.BUTTON2_MASK) != 0) {
processMiddle(evt.getPoint());
}
if ((evt.getModifiers() &
InputEvent.BUTTON3_MASK) != 0) {
processRight(evt.getPoint());
}
}
}
Handling Mouse Motion
component.addMouseMotionListener(
new MyMouseMotionListener());
public class MyMouseMotionListener
extends MouseMotionAdapter {
public void mouseMoved(MouseEvent evt) {
// Process current position of cursor
// while all mouse buttons are up.
process(evt.getPoint());
}
public void mouseDragged(MouseEvent evt) {
// Process current position of cursor
// while mouse button is pressed.
process(evt.getPoint());
}
}
Detecting Double and Triple Clicks
component.addMouseListener(
new MyMouseListener());
public class MyMouseListener extends MouseAdapter {
public void mouseClicked(MouseEvent evt) {
if (evt.getClickCount() == 3) {
// triple-click
} else if (evt.getClickCount() == 2) {
// double-click
}
}
}
Handling Focus Changes
component.addFocusListener(
new MyFocusListener());
public class MyFocusListener
extends FocusAdapter {
public void focusGained(FocusEvent evt) {
// The component gained the focus.
}
public void focusLost(FocusEvent evt) {
// The component lost the focus.
}
}
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