javaswingjscrollpanejscrollbar

How to know if a JScrollBar has reached the bottom of the JScrollPane?


I'd like to know if there is a way to know when a JScrollBar (vertical in my case) has reached the bottom of his containing JScrollPane.

At first i have though of using an AdjustmentListener on the scroll bar but i don't know how to interpret the value attribute of the JScrollBar. Also i'm not sure to properly understand what the maximum represents and if i can use with the value to get the information i need.

Edit:

scrollPane.getVerticalScrollBar().addAdjustmentListener(new AdjustmentListener() {
    @Override
    public void adjustmentValueChanged(AdjustmentEvent ae) {
        System.out.println("Value: " + scrollPane.getVerticalScrollBar().getValue() + " Max: " + scrollPane.getVerticalScrollBar().getMaximum());
    }
}

Solution

  • You have to add the extent of the scrollbar to your calculation. I added the code into your code in the example below.

    scrollPane.getVerticalScrollBar().addAdjustmentListener(new AdjustmentListener() {
        @Override
        public void adjustmentValueChanged(AdjustmentEvent ae) {
            int extent = scrollPane.getVerticalScrollBar().getModel().getExtent();
            System.out.println("Value: " + (scrollPane.getVerticalScrollBar().getValue()+extent) + " Max: " + scrollPane.getVerticalScrollBar().getMaximum());
        }
    });
    

    Two alternative implementations (partially reacting to Kleopatra)

    scrollPane.getVerticalScrollBar().addAdjustmentListener(new AdjustmentListener() {
    
        @Override
        public void adjustmentValueChanged(AdjustmentEvent event) {
            JScrollBar scrollBar = (JScrollBar) event.getAdjustable();
            int extent = scrollBar.getModel().getExtent();
            System.out.println("1. Value: " + (scrollBar.getValue() + extent) + " Max: " + scrollBar.getMaximum());
    
        }
    });
    

    Or via the model

    scrollPane.getVerticalScrollBar().getModel().addChangeListener(new ChangeListener() {
    
        @Override
        public void stateChanged(ChangeEvent event) {
            BoundedRangeModel model = (BoundedRangeModel) event.getSource();
            int extent = model.getExtent();
            int maximum = model.getMaximum();
            int value = model.getValue();
    
            System.out.println("2. Value: " + (value + extent) + " Max: " + maximum);
    
        }
    });