package jcomboboxdemo;import java.awt.*;import java.awt.event.*;import javax.swing.*;/** * <p>Title: </p> * <p>Description: </p> * <p>Copyright: Copyright (c) 2002</p> * <p>Company: </p> * @author unascribed * @version 1.0 */public class MainFrame extends JFrame {  private JPanel contentPane;  private BorderLayout borderLayout1 = new BorderLayout();  private JLabel jLabel1 = new JLabel();  private JComboBox jComboBox1 = new JComboBox();  private String[] defaultSites={        "http://www.pku.edu.cn",        "http://www.edu.cn",        "http://e.pku.edu.cn",        "http://www.tsinghua.edu.cn",        "http://www.google.com"  };  private String defaultEdit="http://www.pku.edu.cn";  //Construct the frame  public MainFrame() {    enableEvents(AWTEvent.WINDOW_EVENT_MASK);    try {      jbInit();    }    catch(Exception e) {      e.printStackTrace();    }  }  //Component initialization  private void jbInit() throws Exception  {    //setIconImage(Toolkit.getDefaultToolkit().createImage(MainFrame.class.getResource("[Your Icon]")));    contentPane = (JPanel) this.getContentPane();    jLabel1.setFont(new java.awt.Font("Dialog", 0, 14));    jLabel1.setHorizontalAlignment(SwingConstants.CENTER);    jLabel1.setText("  地  址：");    contentPane.setLayout(borderLayout1);    this.setSize(new Dimension(468, 59));    this.setTitle("JComboBoxDemo");    jComboBox1.setFont(new java.awt.Font("Dialog", 0, 14));    jComboBox1.setEditable(true);    jComboBox1.setMaximumRowCount(5);    jComboBox1.addActionListener(new java.awt.event.ActionListener() {      public void actionPerformed(ActionEvent e) {        jComboBox1_actionPerformed(e);      }    });    jComboBox1.configureEditor(jComboBox1.getEditor(),defaultEdit);    ComboBoxEditor comboxEditor=jComboBox1.getEditor();    Component editorComp = comboxEditor.getEditorComponent();    editorComp.setBackground(Color.white);    editorComp.setForeground(Color.red);    editorComp.setFont(new Font("Dialog",Font.PLAIN,14));    contentPane.add(jLabel1, BorderLayout.WEST);    contentPane.add(jComboBox1, BorderLayout.CENTER);  }  //Overridden so we can exit when window is closed  protected void processWindowEvent(WindowEvent e) {    super.processWindowEvent(e);    if (e.getID() == WindowEvent.WINDOW_CLOSING) {      System.exit(0);    }  }  void jComboBox1_actionPerformed(ActionEvent e) {    boolean isItemPresent = false;    for(int i=0;i<jComboBox1.getItemCount();i++)    {        if(jComboBox1.getItemAt(i).equals(jComboBox1.getSelectedItem())){                isItemPresent=false;                break;        }    }    if(!isItemPresent){        jComboBox1.insertItemAt(jComboBox1.getSelectedItem(),0);        isItemPresent=false;    }  }}