listdemo.java

来自「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」· Java 代码 · 共 89 行

// ListDemo.java: Use list to select a country and display the
// selected country's flag
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;

public class ListDemo extends JFrame implements ListSelectionListener
{
  // Declare an ImageIcon array for the national flags of 9 countries
  private ImageIcon[] imageIcon = new ImageIcon[9];

  // Arrays of labels for displaying images
  private JLabel[] jlblImageViewer = new JLabel[9];

  // The list for selecting countries
  JList jlst;

  // Main Method
  public static void main(String[] args)
  {
    ListDemo frame = new ListDemo();
    frame.setSize(650, 500);
    frame.setTitle("List Demo");
    // frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);
  }

  // Default Constructor
  public ListDemo()
  {
    // Load images into imageIcon array
    imageIcon[0] = new ImageIcon("images/us.gif");
    imageIcon[1] = new ImageIcon("images/ca.gif");
    imageIcon[2] = new ImageIcon("images/uk.gif");
    imageIcon[3] = new ImageIcon("images/germany.gif");
    imageIcon[4] = new ImageIcon("images/fr.gif");
    imageIcon[5] = new ImageIcon("images/denmark.gif");
    imageIcon[6] = new ImageIcon("images/norway.gif");
    imageIcon[7] = new ImageIcon("images/china.gif");
    imageIcon[8] = new ImageIcon("images/india.gif");

    // Create a string of country names
    String[] countries = {"United States of America", "Canada",
      "United Kingdom", "Germany", "France", "Denmark", "Norway",
      "China", "India"};

    // Create a list with the country names
    jlst = new JList(countries);

    // Create a panel to hold nine labels
    JPanel p = new JPanel();
    p.setLayout(new GridLayout(3, 3));

    for (int i=0; i<9; i++)
    {
      p.add(jlblImageViewer[i] = new JLabel());
      jlblImageViewer[i].setHorizontalAlignment
        (SwingConstants.CENTER);
    }

    // Add p and the list to the frame
    getContentPane().add(p, BorderLayout.CENTER);
    getContentPane().add(new JScrollPane(jlst), BorderLayout.WEST);

    // Register listeners
    jlst.addListSelectionListener(this);
  }

  // Handle list selection
  public void valueChanged(ListSelectionEvent e)
  {
    // Get selected indices
    int[] indices = jlst.getSelectedIndices();
 
    int i;
    // Set icons in the labels
    for (i=0; i<indices.length; i++)
    {
      jlblImageViewer[i].setIcon(imageIcon[indices[i]]);
    }

    // Remove icons from the rest of the labels
    for (; i<9; i++)
    {
      jlblImageViewer[i].setIcon(null);
    }
  }
}