showcardlayout.java

此源码为机械工业出版社出版的《Java语言程序设计》第三版所配套的书中所有源代码。

// ShowCardLayout.java: Using CardLayout to display images
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class ShowCardLayout extends JApplet
  implements ActionListener, ItemListener
{
  private CardLayout queue = new CardLayout();
  private JPanel cardPanel = new JPanel();
  private JButton jbtFirst, jbtNext, jbtPrevious, jbtLast;
  private JComboBox jcboImage;

  public void init()
  {
    // Use CardLayout for cardPanel
    cardPanel.setLayout(queue);

    // Add 15 labels for displaying images into cardPanel
    for (int i=1; i<=15; i++)
      cardPanel.add
        (new JLabel(new ImageIcon("images/L"+i+".gif")),
          String.valueOf(i));

    // Panel p to hold buttons and a combo box
    JPanel p = new JPanel();
    p.add(jbtFirst = new JButton("First"));
    p.add(jbtNext = new JButton("Next"));
    p.add(jbtPrevious= new JButton("Previous"));
    p.add(jbtLast = new JButton("Last"));
    p.add(new JLabel("Image"));
    p.add(jcboImage = new JComboBox());

    // Initialize combo box items
    for (int i=1; i<=15; i++)
      jcboImage.addItem(String.valueOf(i));

    // Place panels in the frame
    getContentPane().add(cardPanel, BorderLayout.CENTER);
    getContentPane().add(p, BorderLayout.NORTH);

    // Register listeners with the source objects
    jbtFirst.addActionListener(this);
    jbtNext.addActionListener(this);
    jbtPrevious.addActionListener(this);
    jbtLast.addActionListener(this);
    jcboImage.addItemListener(this);
  }

  // This main method enables the applet to run as an application
  public static void main(String[] args)
  {
    // Create a frame
    JFrame frame = new JFrame("CardLayout Demo");

    // Create an instance of the applet
    ShowCardLayout applet = new ShowCardLayout();

    // Add the applet instance to the frame
    frame.getContentPane().add(applet, BorderLayout.CENTER);

    // Invoke init() and start()
    applet.init();
    applet.start();

    // Display the frame
    frame.setSize(300, 300);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);
  }

  // Handle button actions
  public void actionPerformed(ActionEvent e)
  {
    String actionCommand = e.getActionCommand();
    if (e.getSource() instanceof JButton)
      if ("First".equals(actionCommand))
        // Show the first component in queue
        queue.first(cardPanel);
      else if ("Last".equals(actionCommand))
        // Show the last component in queue
        queue.last(cardPanel);
      else if ("Previous".equals(actionCommand))
        // Show the previous component in queue
        queue.previous(cardPanel);
      else if ("Next".equals(actionCommand))
        // Show the next component in queue
        queue.next(cardPanel);
  }

  // Handle selection of combo box item
  public void itemStateChanged(ItemEvent e)
  {
    if (e.getSource() == jcboImage)
      // Show the component at specified index
      queue.show(cardPanel, (String)e.getItem());
  }
}