listdataeventdemo.java

《java事件处理指南》一书的代码,好东西

import javax.swing.*;
import javax.swing.event.*;
import java.awt.*;
import java.awt.event.*;

public class ListDataEventDemo extends JFrame implements ActionListener
{
   private JButton button;
   private JTextField jtf;
   private JList list;
   private DefaultListModel model;

   public ListDataEventDemo() 
   {
/*  A JList object is created by first initializing a DefaultListModel  */
/*  with a list of names.  The DefaultListModel registers a             */
/*  ListDataListener.                                                   */

      model = new DefaultListModel();
      model.addElement("Mark");
      model.addElement("Maria");
      model.addElement("Scott");
      model.addElement("Diana");
      model.addElement("Stephanie");
      model.addListDataListener(new ListDataHandler());

      list = new JList(model);
      list.setVisibleRowCount(7);

      button = new JButton("Add");
      button.setBorder(BorderFactory.createRaisedBevelBorder());
      button.addActionListener(this);

      jtf = new JTextField(15);
      jtf.setBorder(BorderFactory.createLineBorder(Color.black));

      JPanel centerPanel = new JPanel();
      centerPanel.add(new JScrollPane(list,
                 ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS,
                 ScrollPaneConstants.HORIZONTAL_SCROLLBAR_AS_NEEDED));

      JPanel southPanel = new JPanel();
      southPanel.add(jtf);
      southPanel.add(button);

      getContentPane().add(centerPanel, BorderLayout.CENTER);
      getContentPane().add(southPanel, BorderLayout.SOUTH);

      setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      setBounds(100, 100, 300, 300);
      setVisible(true);
   }

/*  When the "Add" button is pressed, the text in the JTextField is  */
/*  added as an element to the JList.                                */

   public void actionPerformed(ActionEvent event)
   {
      if ( jtf.getText().length() != 0 )
      {
         model.addElement(jtf.getText());
      }
   }

/*  The ListDataListener is implemented as an inner class.  Whenever   */
/*  an element is added to the list, a ListDataEvent is generated and  */
/*  sent to the intervalAdded() method.  This method checks to see if  */
/*  the element is already in the list.  If it is, the element is      */
/*  removed.  This action generates another ListDataEvent that is      */
/*  sent to the intervalRemoved() method.  This method displays a      */
/*  message dialog informing the user that the name is already part    */
/*  of the list.                                                       */

   class ListDataHandler implements ListDataListener
   {
      public void intervalAdded(ListDataEvent event)
      {
         for(int i=0; i<event.getIndex0(); ++i)
         {
            String element = (String)model.elementAt(i);
            String newElement = (String)model.elementAt(event.getIndex0());
            if ( newElement.equals(element) )
            {
               model.removeElementAt(event.getIndex0());
               break;
            }
         }
         jtf.setText("");
      }

      public void intervalRemoved(ListDataEvent event)
      {
         JOptionPane.showMessageDialog(list, "Name already in list");
      }

      public void contentsChanged(ListDataEvent event) {}
   }

   public static void main(String args[]) 
   {
      ListDataEventDemo demo = new ListDataEventDemo();
   }
}