What exactly does getValueIsAdjusting do?

Question

As you know, without using !getValueIsAdjusting when you select a row in a jtable (by clicking) the selection change event fire twice. It doesn't happen if you select a row using the keyboard arrow. To resolve it, you check if getValueIsAdjusting returns false.

My question is why does the event fire twice if I select a row by clicking it, but not when using the keyboard arrow? And what does getValueIsAdjusting do to resolve it?

Answer 1

As the javadoc which JB Nizet linked to states, getValueIsAdjusting() checks whether a specific event (a change) is part of a chain, if so it will return true. It will only return false when the specified event is the final one in the chain.

In your case, selecting a row by clicking actually fires two events: a mouseDown and mouseUp event and both are sent to your event listener. If you correctly implement getValueIsAdjusting() to return whenever the value is true, you will only act on the final event in the chain, which is the mouseUp event that fires when you let go of the left mouse button.

The Java Tutorials include an example that captures events, you can use that to log the selection events and experiment with it yourself. Remove the return on the event.getValueIsAdjusting() check to log every event that's fired.

Answer 2

    String interessen[]= {"aaaaaaa", "bbbbbbbb", "ccccccccc", "ddddddd"};

    myList = new JList<>(interessen);

    myList.addListSelectionListener(new ListSelectionListener() {


        @Override
        public void valueChanged(ListSelectionEvent e) {
            if(!e.getValueIsAdjusting())
            System.out.println(myList.getSelectedValue());

        }
    });

The code above shows what getValueIsAdjusting do, without these method an event may be called eg. two times (it depends of event).

Output without getValueIsAdjusting loop after clicking on some element of JList: aaaaaaa aaaaaaa

with loop: aaaaaaa