Layout Management and GUI Components - Learning Java Through Games - page 272

}

}

class ConverterFrame extends JFrame {

public ConverterFrame () {
setDefaultCloseOperation(JFrame.DISPOSEON CLOSE) ;
setLayout( new BorderLayout () ) ; //not required
JPanel cPanel = new JPanel () ;
JPanel fPanel = new JPanel () ;
JPanel buttonPanel = new JPanel () ;
final JTextField cField = new JTextField(20) ;
final JTextField fField = new JTextField(20) ;
cPanel .add( new JLabel( "Celsius: " ));
cPanel .add( cField) ;
fPanel .add( new JLabel( "Fahrenheit: " ));
fPanel .add( fField) ;
JButton convertButton = new JButton( "CONVERT" );
buttonPanel .add(convertButton) ;
add(cPanel , BorderLayout .NORTH) ;
add( fPanel , BorderLayout .CENTER) ;
add(buttonPanel , BorderLayout .SOUTH) ;
convertButton . addActionListener( new ActionListener ()

{

public void actionPerformed(ActionEvent e) {
if (cField.getText().trim().equals( "" ) && fField . getText () . trim
() . equals( "" )) {
return ;
if (cField.getText().trim().equals( "" )) {
String result = fField.getText() .trim() ;
double number = Double . parseDouble ( r e su l t ) ;
number = (number − 32) ∗ (5/9.0) ;
cField . setText( "" + number) ;
if ( fField . getText () . trim() . equals ( "" )) {
String result = cField.getText() .trim() ;
double number = Double . parseDouble ( r e su l t ) ;
number = number ∗ (9 / 5.0) + 32;
fField .setText( "" + number) ;

}

}

} );

pack() ;

}

}

The code creates three panels: in the north, center, and south. In each panel, several
components are added. Since the default layout for a panel is the flow layout, the components
are added in the panel using the flow layout (i.e., they are placed from left to right inside the
panel). The actionPerformed method is associated with the CONVERT button. The method
first checks if both the Celsius and Fahrenheit text fields are empty. If this is the case, then
there is nothing to do. If only one of them is empty, then its value is calculated based on
the value of the other field. The parseDouble static method of the Double classisusedto
convert a String to a double .Thereisalsoa parseInt static method in the class Integer
that converts a string to an integer. If the conversion fails, that is, the input is not a number,
then an exception is raised. The setText method is used to set the new value of the text