A scrollbar in a scroll pane fires adjustment events whenever its value changes.

    // Create a scrollable text area

    JTextArea textArea = new JTextArea();

    JScrollPane pane = new JScrollPane(textArea);

    // Listen for value changes in the scroll pane's scrollbars

    AdjustmentListener listener = new MyAdjustmentListener();

    pane.getHorizontalScrollBar().addAdjustmentListener(listener);

    pane.getVerticalScrollBar().addAdjustmentListener(listener);

    class MyAdjustmentListener implements AdjustmentListener {

        // This method is called whenever the value of a scrollbar is changed,

        // either by the user or programmatically.

        public void adjustmentValueChanged(AdjustmentEvent evt) {

            Adjustable source = evt.getAdjustable();

            // getValueIsAdjusting() returns true if the user is currently

            // dragging the scrollbar's knob and has not picked a final value

            if (evt.getValueIsAdjusting()) {

                // The user is dragging the knob

                return;

            }

            // Determine which scrollbar fired the event

            int orient = source.getOrientation();

            if (orient == Adjustable.HORIZONTAL) {

                // Event from horizontal scrollbar

            } else {

                // Event from vertical scrollbar

            }

            // Determine the type of event

            int type = evt.getAdjustmentType();

            switch (type) {

              case AdjustmentEvent.UNIT_INCREMENT:

                  // Scrollbar was increased by one unit

                  break;

              case AdjustmentEvent.UNIT_DECREMENT:

                  // Scrollbar was decreased by one unit

                  break;

              case AdjustmentEvent.BLOCK_INCREMENT:

                  // Scrollbar was increased by one block

                  break;

              case AdjustmentEvent.BLOCK_DECREMENT:

                  // Scrollbar was decreased by one block

                  break;

              case AdjustmentEvent.TRACK:

                  // The knob on the scrollbar was dragged

                  break;

            }

            // Get current value

            int value = evt.getValue();

        }

    }