ItemListener is an interface in the Java programming language that defines a listener for item events. An ItemEvent occurs when an item is selected or deselected in a component such as a JCheckBox, JRadioButton, or JComboBox.

To use an ItemListener, you typically create an instance of a class that implements the ItemListener interface and then register it with the component that generates item events, such as a JCheckBox or JComboBox. For example, to create an ItemListener for a JCheckBox, you might write:

JCheckBox checkBox = new JCheckBox("Select me");
checkBox.addItemListener(new ItemListener() {
    public void itemStateChanged(ItemEvent e) {
        if (e.getStateChange() == ItemEvent.SELECTED) {
            // Perform some action when the checkbox is selected
        } else if (e.getStateChange() == ItemEvent.DESELECTED) {
            // Perform some action when the checkbox is deselected
        }
    }
});

This code creates an anonymous inner class that implements the ItemListener interface and defines the itemStateChanged method for handling item events. The getStateChange method of the ItemEvent object passed to this method returns either ItemEvent.SELECTED or ItemEvent.DESELECTED, depending on whether the item was selected or deselected.

In Java 8 and later, you can use lambda expressions to define ItemListener instances more concisely. For example:

JCheckBox checkBox = new JCheckBox("Select me");
checkBox.addItemListener(e -> {
    if (e.getStateChange() == ItemEvent.SELECTED) {
        // Perform some action when the checkbox is selected
    } else if (e.getStateChange() == ItemEvent.DESELECTED) {
        // Perform some action when the checkbox is deselected
    }
});

This code creates an ItemListener instance using a lambda expression instead of an anonymous inner class. The lambda expression takes an ItemEvent parameter and performs the desired action based on the state change of the item.