/* Most of the code immediately below is just copied from SwingHelloWorld.java */ import javax.swing.*; /* This is new; we need stuff from the awt packages so that we can process * user input. */ import java.awt.*; import java.awt.event.*; public class SwingInputDemo3b implements Runnable { /* This is new; instance variables to hold JTextBox and JButton components */ private JTextField textBox_; private JButton okButton_; private JButton clearButton_; private JButton exitButton_; public static void main( String[] args ) { SwingInputDemo3b demo = new SwingInputDemo3b(); SwingUtilities.invokeLater( demo ); } public void run() { createGUI(); } private void createGUI() { JFrame frame = new JFrame( "Swing Input Demo 3b" ); frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE ); /* I chose to do the layout in a separate method so that it will be * easier to see the logic that is used to set up the OK button to * tell us when it is clicked. The doLayout method will create all * the components and arrange them within the JFrame. */ doLayout( frame ); /* This is how we set up the OK, Clear and Exit buttons so that we * will know when they are clicked. "OKButtonListener," * "ClearButtonListener" and "ExitButtonListener" are private classes * that we define below. This differs from "Swing Input Demo 3a" in * that we use a single ActionListener for all three buttons. */ ButtonListener listener = new ButtonListener(); okButton_.addActionListener( listener ); clearButton_.addActionListener( listener ); exitButton_.addActionListener( listener ); /* This time we won't bother to add a listener to the text box. We * will just wait until the OK button is clicked, then we will * display whatever was typed into the text box in a JOptionPane. */ /* Show the dialog. */ frame.setVisible( true ); } /************************************************************************** * The doLayout Method * =================== * This is an enhancement of the layout demonstrated in * "SwingInputDemo2.java." Two buttons are added to the dialog, centered * beneath the label and text box components. * * +---------------------------------------+ * | | * | label text box | * | | * | OK Clear Exit | * | | * +---------------------------------------+ * * In order to center the row of buttons we will put them in a JPanel * then use a GridBagLayout in the frame to center the JPanel below the * label and text box. The GridBagLayout will consist of two rows and * two columns; the label ("Swing Input Demo 3b") goes in the cell (0,0), * the text box goes in cell (0,1), and the panel occupies both cells (1,0) * and (1,1). Each cell will be separated from the inside of the frame and * each other (that is, they will be "inset") by a margin of 5 pixels. * * +-----------------------------------+ * | | | * | | | * | label | text box | * | | | * | | | * |-----------------+-----------------| * | | | * | +---------------------------+ | * | | JPa|nel | | * | +---------------------------+ | * | | | * +-----------------------------------+ * * By default, the three buttons will be made just big enough to contain * their names, which will make them different sizes. In order to make them * all the same size a GridLayout consisting of one row and three columns * is added to the panel. * * +---------------------------+ * | OK | Clear | Exit | * +---------------------------+ **************************************************************************/ private void doLayout( JFrame frame ) { /* The panel is used to center the row of buttons in the frame. Its * layout manager is a GridLayout with 1 row, 3 columns, a horizontal * margin of 5 pixels and a vertical margin of 0. */ JPanel panel = new JPanel ( new GridLayout( 1, 3, 5, 0 ) ); JLabel label = new JLabel( "Swing Input Demo 3b" ); textBox_ = new JTextField( 20 ); okButton_ = new JButton( "OK" ); clearButton_ = new JButton( "Clear" ); exitButton_ = new JButton( "Exit" ); /* Most of the work we need to do requires manipulation of the * container component of the frame. */ Container container = frame.getContentPane(); /* Create and set the GridBagLayout manager. */ container.setLayout( new GridBagLayout() ); /* A GridBagConstraints object is used to determine the cell position * of the label, text box and button panel. */ GridBagConstraints gbc = new GridBagConstraints(); /* The fill constraint determines how a component is resized if it is * too small to fit in its cell. We don't want the component resized * at all. */ gbc.fill = GridBagConstraints.NONE; /* The insets constraint determines the margins. */ gbc.insets = new Insets( 5, 5, 5, 5 ); /* The label goes in cell (0,0). */ gbc.gridx = 0; gbc.gridy = 0; container.add( label, gbc ); /* The text box goes in cell (1,0). */ gbc.gridx = 1; gbc.gridy = 0; container.add( textBox_, gbc ); /* The panel starts in cell (0,1), and spans two cells. */ gbc.gridx = 0; gbc.gridy = 1; gbc.gridwidth = 2; container.add( panel, gbc ); panel.add( okButton_ ); panel.add( clearButton_ ); panel.add( exitButton_ ); /* Tell the layout manager to perform the layout. */ frame.pack(); } /************************************************************************** * The ButtonListener Class * ======================== * We need an object of this type to "listen" for events that occur in * the a button. The "implements ActionListener" is a promise to the * compiler to have a "public void actionPerformed( ActionEvent )" * method. */ private class ButtonListener implements ActionListener { /* This method is called when a button is clicked. */ public void actionPerformed( ActionEvent event ) { Object obj = event.getSource(); if ( obj == okButton_ ) { String msg = "text: " + textBox_.getText(); JOptionPane.showMessageDialog( null, msg ); } else if ( obj == clearButton_ ) { textBox_.setText( "" ); } else if ( obj == exitButton_ ) { String msg = "Are you sure you want to exit?"; int option = JOptionPane.showConfirmDialog( null, msg, "Swing Input Demo 3b", JOptionPane.YES_NO_OPTION ); if ( option == JOptionPane.OK_OPTION ) System.exit( 0 ); } else { String msg = "Error: mystery button click."; JOptionPane.showMessageDialog( null, msg, "Swing Input Demo 3b", JOptionPane.WARNING_MESSAGE ); } } } }