listdemo.java

用户可以在列表中选择国家

// 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
{
  // 声明引用图像数组的变量，并初始化变量
  private ImageIcon[] imageIcon = new ImageIcon[9];
	
  // 声明引用标签数组的变量
  private JLabel[] jlblImageViewer = new JLabel[9];

  // 声明列表框变量
  JList jlst;

  // 主方法
  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()
  {
    // 对图像数组元素初始化
    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");

    // 声明引用字符串数组的变量 country， 并对字符串数组元素初始化
    String[] countries = {"United States of America", "Canada", "United Kingdom", "Germany", "France", "Denmark", "Norway",  "China", "India"};

    // 用字符串数组为参数，创建一个列表框
    jlst = new JList(countries);

    //创建一个容纳9个标签的面板
    JPanel p = new JPanel();
    p.setLayout(new GridLayout(3, 3));

    //对标签数组元素初始化
    for (int i=0; i<9; i++)
    {
      p.add(jlblImageViewer[i] = new JLabel());
      jlblImageViewer[i].setHorizontalAlignment(SwingConstants.CENTER);
    }

    //把面板和列表框加入框架
    getContentPane().add(p, BorderLayout.CENTER);
    getContentPane().add(new JScrollPane(jlst), BorderLayout.WEST);

    // 为列表框注册监听器
    jlst.addListSelectionListener(this);
  }

  //处理列表框事件的处理器
  public void valueChanged(ListSelectionEvent e)
  {
    // 获取列表框中，被选择的选项的索引号，保存在数组 indices中
    int[] indices = jlst.getSelectedIndices();
 
    int i;
    // 为对应索引号的标签设置图像对象
    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);
    }
  }
}