Java Tutorial/Swing Event/ItemListener

ComboBox with ItemListener

import java.awt.BorderLayout;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class ComboBoxWithItemChangedListener extends JFrame {
  public static void main(String[] args) {
    ComboBoxWithItemChangedListener that = new ComboBoxWithItemChangedListener();
    that.setVisible(true);
  }
  public ComboBoxWithItemChangedListener() {
    setSize(450, 350);
    this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    getContentPane().add(new ComboPanel(), BorderLayout.SOUTH);
  }
}
class ComboPanel extends JPanel {
  final static String[] treasure = { "Gold", "Silver", "Diamonds", "Rubies", "Emeralds",
      "Sapphires", "Chocolate" };
  public ComboPanel() {
    final JComboBox combo = new JComboBox(treasure);
    combo.setMaximumRowCount(5);
    combo.addItemListener(new ItemListener() {
      public void itemStateChanged(ItemEvent e) {
        System.out.println("Combo: " + combo.getSelectedItem());
      }
    });
    combo.setSelectedIndex(4);
    add(combo);
  }
}

Firing Item Events

import java.awt.ItemSelectable;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.event.EventListenerList;
public class Main {
  public static void main(String[] argv) throws Exception {
    MyComponent component = new MyComponent();
    JFrame f = new JFrame();
    f.add(component);
    f.setSize(300, 300);
    f.setVisible(true);
  }
}
class MyComponent extends JTextField implements ItemSelectable {
  protected EventListenerList listenerList = new EventListenerList();
  public Object[] getSelectedObjects() {
    return new String[] { "a", "b", "c" };
  }
  public void addItemListener(ItemListener l) {
    listenerList.add(ItemListener.class, l);
  }
  public void removeItemListener(ItemListener l) {
    listenerList.remove(ItemListener.class, l);
  }
  void fireItemEvent(Object item, boolean sel) {
    ItemEvent evt = new ItemEvent(this, ItemEvent.ITEM_STATE_CHANGED, item,
        sel ? ItemEvent.SELECTED : ItemEvent.DESELECTED);
    Object[] listeners = listenerList.getListenerList();
    for (int i = 0; i < listeners.length - 2; i += 2) {
      if (listeners[i] == ItemListener.class) {
        ((ItemListener) listeners[i + 1]).itemStateChanged(evt);
      }
    }
  }
}

How to Write an Item Listener

import java.awt.Color;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import javax.swing.AbstractButton;
import javax.swing.JCheckBox;
import javax.swing.JFrame;
public class JCheckBoxItemListener {
  public static void main(String args[]) {
    JFrame frame = new JFrame("Iconizing CheckBox");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    JCheckBox aCheckBox4 = new JCheckBox("Stuffed Crust");
    ItemListener itemListener = new ItemListener() {
      public void itemStateChanged(ItemEvent itemEvent) {
        AbstractButton abstractButton = (AbstractButton)itemEvent.getSource();
        Color foreground = abstractButton.getForeground();
        Color background = abstractButton.getBackground();
        int state = itemEvent.getStateChange();
        if (state == ItemEvent.SELECTED) {
          abstractButton.setForeground(background);
          abstractButton.setBackground(foreground);
        }
      }
    };
    aCheckBox4.addItemListener(itemListener);
    frame.add(aCheckBox4);
    frame.setSize(300, 200);
    frame.setVisible(true);
  }
}

ItemListener for JRadioButton

import java.awt.BorderLayout;
import java.awt.ruponent;
import java.awt.Container;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import javax.swing.ButtonGroup;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
import javax.swing.WindowConstants;
public class Main extends JFrame {
  private JRadioButton small, medium, large;
  private JButton button;
  public Main(String title) {
    super(title);
    this.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
    Container contentPane = this.getContentPane();
    ButtonGroup group = new ButtonGroup();
    small = new JRadioButton("small");
    medium = new JRadioButton("medium");
    large = new JRadioButton("large");
    group.add(small);
    group.add(medium);
    group.add(large);
    button = new JButton("Click here.");
    button.setBounds(100, 50, 100, 50);
    JPanel center = new JPanel();
    center.setLayout(null);
    center.add(button);
    contentPane.add(center, BorderLayout.CENTER);
    JPanel north = new JPanel();
    north.add(small);
    north.add(medium);
    north.add(large);
    contentPane.add(north, BorderLayout.NORTH);
    ChangeSize listener = new ChangeSize(button);
    small.addItemListener(listener);
    medium.addItemListener(listener);
    large.addItemListener(listener);
  }
  public static void main(String[] args) {
    JFrame f = new Main("JRadioButtonDemo");
    f.setSize(300, 200);
    f.setVisible(true);
  }
}
class ChangeSize implements ItemListener {
  private Component component;
  public ChangeSize(Component c) {
    component = c;
  }
  public void itemStateChanged(ItemEvent e) {
    String size = (String) e.getItem();
    if (size.equals("small")) {
      component.setSize(75, 20);
    } else if (size.equals("medium")) {
      component.setSize(100, 50);
    } else if (size.equals("large")) {
      component.setSize(150, 75);
    }
  }
}

Toggle button with ItemListener

import java.awt.BorderLayout;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.AbstractButton;
import javax.swing.ButtonGroup;
import javax.swing.JCheckBox;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
import javax.swing.JToggleButton;
public class ToggleButtonCheckBoxRadioButton extends JFrame {
  public static void main(String[] args) {
    ToggleButtonCheckBoxRadioButton that = new ToggleButtonCheckBoxRadioButton();
    that.setVisible(true);
  }
  public ToggleButtonCheckBoxRadioButton() {
    setSize(450, 350);
    this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    getContentPane().add(new TogglePanel(), BorderLayout.SOUTH);
  }
}
class TogglePanel extends JPanel {
  public TogglePanel() {
    JToggleButton tog = new JToggleButton("Toggle");
    ItemListener listener = new ItemListener() {
      public void itemStateChanged(ItemEvent e) {
        AbstractButton src = (AbstractButton) (e.getSource());
        System.out.println("Toggle: " + src.getText());
      }
    };
    tog.addItemListener(listener);
    add(tog);
    JCheckBox cbox = new JCheckBox("Checkbox");
    cbox.addItemListener(listener);
    add(cbox);
    ButtonGroup btngroup = new ButtonGroup();
    for (int i = 1; i <= 3; i++) {
      JRadioButton radio = new JRadioButton("Radio " + i);
      btngroup.add(radio);
      radio.addItemListener(listener);
      add(radio);
    }
  }
}