selectingcombosample.java

The Definitive Guide to Java Swing, Third Edition by John Zukowski (Author) 源码

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

public class SelectingComboSample {
  static private String selectedString(ItemSelectable is) {
    Object selected[] = is.getSelectedObjects();
    return ((selected.length == 0) ? "null" : (String)selected[0]);
  }

  public static void main(String args[]) {
    Runnable runner = new Runnable() {
      public void run() {
        String labels[] = {"Chardonnay", "Sauvignon", "Riesling", "Cabernet",
          "Zinfandel", "Merlot", "Pinot Noir", "Sauvignon Blanc", "Syrah",
          "Gew黵ztraminer"};
        JFrame frame = new JFrame("Selecting JComboBox");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JComboBox comboBox = new JComboBox(labels);
        frame.add(comboBox, BorderLayout.SOUTH);

        final JTextArea textArea = new JTextArea();
        textArea.setEditable(false);
        JScrollPane sp = new JScrollPane(textArea);
        frame.add(sp, BorderLayout.CENTER);

        ItemListener itemListener = new ItemListener() {
          public void itemStateChanged(ItemEvent itemEvent) {
            StringWriter sw = new StringWriter();
            PrintWriter pw = new PrintWriter(sw);
            int state = itemEvent.getStateChange();
            String stateString = 
              ((state == ItemEvent.SELECTED) ? "Selected" : "Deselected");
            pw.print("Item: " + itemEvent.getItem());
            pw.print(", State: " + stateString);
            ItemSelectable is = itemEvent.getItemSelectable();
            pw.print(", Selected: " + selectedString(is));
            pw.println();
            textArea.append(sw.toString());
          }
        };
        comboBox.addItemListener(itemListener);

        ActionListener actionListener = new ActionListener() {
          public void actionPerformed(ActionEvent actionEvent) {
            StringWriter sw = new StringWriter();
            PrintWriter pw = new PrintWriter(sw);
            pw.print("Command: " + actionEvent.getActionCommand());
            ItemSelectable is = (ItemSelectable)actionEvent.getSource();
            pw.print(", Selected: " + selectedString(is));
            pw.println();
            textArea.append(sw.toString());
          }
        };
        comboBox.addActionListener(actionListener);

        frame.setSize(400, 200);
        frame.setVisible(true);
      }
    };
    EventQueue.invokeLater(runner);
  }
}