How to work with the scroll bar in Swing

Overview

The class JScrollBar represents the scroll bar in Swing. The scroll bar is used to determine the viewing area of the component in Swing. The scroll bar involves a knob that can be adjusted by the user and that shows the displayable contents of the component.

The scroll bar has the following properties that specify the position of the knob and the scroll bar track:

  • orientation: This indicates a horizontal or a vertical Scrollbar.
  • value: This indicates the model’s current value. The upper limit on the model’s value is maximum - extent and the lower limit is minimum.
  • extent: This indicates the width of the knob of the scrollbar.
  • minimum: This indicates the minimum width of the track on which the scrollbar moves.
  • maximum: This indicates the maximum width of the track on which the scrollbar moves.

All the properties above are bundled into a model.

Constructors of JScrollBar

The different constructors of JScrollBar that can be used while creating a JScrollBar object are as follows:

  1. JScrollBar()

This constructor is used to construct a JScrollBar object with the following initial values:

  • minimum = 0
  • maximum = 100
  • value = 0
  • extent = 10
  1. JScrollBar(int orientation)

This constructor is used to construct a scroll bar with the given orientation. With orientation=0, we get a horizontal scroll bar, and with orientation=1, we get a vertical scroll bar.

  1. JScrollBar(int orientation, int value, int extent, int min, int max)

This constructor is used to construct a JScrollBar object with the given properties.

Commonly used methods of JScrollBar class

The most commonly used methods of the JScrollBar class are as follows:

  1. The addAdjustmentListener(AdjustmentListener l) method adds a listener to the specified JScrollBar instance. The listener will be notified every time a change to the model of the scroll bar is detected.

  2. The getModel() method returns the model of the scroll bar.

  3. The getMaximum() method returns the maximum value (maximum - extent) of the scrollbar.

  4. The getMinimum() method returns the minimum value of the scroll bar.

  5. The getOrientation() method returns the orientation of the scroll bar.

  6. The getValue() method returns the scrollbar’s value.

  7. The setMaximum() method is used to set the maximum value of the scrollbar.

  8. The setMinimum() method is used to set the minimum value of the scroll bar.

  9. The setOrientation() method is used to set the orientation of the scroll bar.

  10. The setValue() method is used to set the scrollbar’s value.

Code example

import javax.swing.*;
import java.awt.*;
class Main{
    public static void main(String[] args) {
        final JFrame frame = new JFrame("JScrollbar Demo");
        JScrollBar scrollBarH = new JScrollBar(JScrollBar.HORIZONTAL, 30, 20, 0, 500);
        JScrollBar scrollBarV = new JScrollBar(JScrollBar.VERTICAL, 30, 40, 0, 500);
        frame.setSize(300,200);
        frame.getContentPane().add(scrollBarH, BorderLayout.SOUTH);
        frame.getContentPane().add(scrollBarV, BorderLayout.EAST);
        frame.setVisible(true);
    }
}

Explanation

Following is the explanation of the given code:

  • Line 7: We create an instance of JFrame called frame.
  • Line 9: We define a horizontal scroll bar scrollBarH.
  • Line 10: We define a vertical scroll bar scrollBarV.
  • Line 12: We set the frame size.
  • Line 13: We add scrollBarH to the frame.
  • Line 14: We add scrollBarV to the frame.
  • Line 15: We set the frame’s visibility to true.

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