How to write an Item Listener in Java?

[shivendra]

Hi friends,
I have recently started doing Java coding. So i am not having much knowledge about the Java. Before that I have done C++ and C# programming languages. Now in Java, I want Item Listener so that item events can be handled. So please tell me how to write an Item Listener in Java.?? Hoping that someone would help me soon.!!

[Solitario]

Since you don't know much about the Item Listener, I think you should know the basic concepts about that. Otherwise you will find hard while doing the coding. Item events are fired by components that implement the ItemSelectable interface. Normally, the on/off state for one or more items are maintained by an ItemSelectable components. Buttons like check boxes, check menu items, toggle buttons, etc are included in the Swing components that fire item events. Hope that you got the point that when exactly to use the Item Listener.!!

[MELTRONICS]

I have provided you with the sample of coding that explains how to write an item-event handling code, have a glace on this code :

checkbox.addItemListener(this);
...
public void itemStateChanged(ItemEvent ie) {
    if (ie.getStateChange() == ItemEvent.SELECTED) {
        label.setVisible(true);
        ...
    } else {
        label.setVisible(false);
    }
}

[Viensterrr]

You should also know the methods that are used for an Item Listener. ItemListener has only one method. So it is not having any corresponding adapter class. The following is the method of an ItemListener Interface :

• itemStateChanged(ItemEvent) - This method is called just after a state change in the listened-to component.

And the following are the methods for an ItemEvent Class :

• Object getItem() - This method returns the component-specific object associated with the item whose state changed.
• getItemSelectable() - This method returns the component that fired the item event.
• int getStateChange() - This method is used for returning the new state of the item.

[kyosang]

You can create a toggle button with the help of an ItemListener. The following code explains the same :

import java.awt.BorderLayout;
import java.awt.event.ItemEvent;
import java.awt.event.WindowAdapter;
import java.awt.event.ItemListener;
import java.awt.event.WindowEvent;
import javax.swing.AbstractButton;
import javax.swing.ButtonGroup;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
import javax.swing.JCheckBox;
import javax.swing.JFrame;
import javax.swing.JToggleButton;

public class ToggleButtonDemo extends JFrame {
  public static void main(String[] args) {
    ToggleButtonDemo that = new ToggleButtonDemo();
    that.setVisible(true);
  }

  public ToggleButtonDemo() {
    setSize(520, 435);

    this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    getContentPane().add(new TogglePanel(), BorderLayout.NORTH);
  }
}

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 <= 4; i++) {
      JRadioButton radio = new JRadioButton("Radio " + i);
      btngroup.add(radio);
      radio.addItemListener(listener);
      add(radio);
    }
  }
}