Why is itemStateChanged on JComboBox is called twice when changed?

Question

I\'m using a JComboBox with an ItemListener on it. When the value is changed, the itemStateChanged event is called twice. The first call, the ItemEvent is showing the origin

Answer 1

Quote from Java Tutorial:

"Only one item at a time can be selected in a combo box, so when the user makes a new selection the previously selected item becomes unselected. Thus two item events are fired each time the user selects a different item from the menu. If the user chooses the same item, no item events are fired."

Answer 2

The code is:

public class Tester {

    private JComboBox box;

    public Tester() {

        box = new JComboBox();
        box.addItem("One");
        box.addItem("Two");
        box.addItem("Three");
        box.addItem("Four");

        box.addItemListener(new ItemListener() {

            public void itemStateChanged(ItemEvent e) {
                if (e.getStateChange() == 1) {

                    JOptionPane.showMessageDialog(box, e.getItem());
                    System.out.println(e.getItem());
                }
            }
        });

        JFrame frame = new JFrame();
        frame.getContentPane().add(box);
        frame.pack();
        frame.setVisible(true);
    }
}

Answer 3

Have a look here,

box.addItemListener(new ItemListener(){
    public void itemStateChanged(ItemEvent e){
        if(e.getStateChange()== ItemEvent.SELECTED) {
            //this will trigger once only when actually the state is changed
            JOptionPane.showMessageDialog(null, "Changed");
        }
    }
});

When you select a new option, it will only once call the JOptionPane, indicating that the code there will be called once only.

Answer 4

private void dropDown_nameItemStateChanged(java.awt.event.ItemEvent evt) {                                                 


    if(evt.getStateChange() == ItemEvent.SELECTED)
    {
        String item = (String) evt.getItem();
        System.out.println(item);
    }

}

Good Luck!