Java AWT Scrollbar

Java AWT (Abstract Window Toolkit) is a collection of libraries for developing responsive and user-friendly interfaces in Java Applications. The Scrollbar is a component that allows us to see an unknown number of rows and columns.

Java AWT Scrollbar

The ‘Scrollbar’ class is a part of the ‘java.awt’ package. Java AWT Scrollbars are used for scrolling through content like text, images, or any other data that doesn’t fit completely within the specified display area. The Scrollbar component supports both vertical and horizontal scrolling. It generates events when it is controlled by the user. We can add custom behavior using different methods to improve the functionality of our application.

Syntax of Java AWT Scrollbar

public class Scrollbar extends Component implements Adjustable, Accessible

Constructors of Java AWT Scrollbar

The table represents the Constructors present in the AWT Scrollbar with a description.

Constructor	Description
Scrollbar()	This constructor creates a new vertical scroll bar as the default one.
Scrollbar(int orientation)	Creates a new scroll bar with the given configuration.
Scrollbar(int orientation, int value, int visible, int minimum, int maximum)	Generates a new scroll bar with the specified direction, minimum and maximum values, visible quantity, and initial value.

The parameters of the given constructors are:

• Orientation: The orientation of the scrollbar specifies whether it will be horizontal or vertical.
• Value: The starting position of the Scrollbar’s knob on its track.
• Minimum: The smallest width of the track on which the scrollbar moves.
• Maximum: The maximum width of the track on which the scrollbar moves.

Fields of Java AWT Scrollbar

The following are the fields of the Scrollbar class:

Modifier and Type	Field	Description
static int	HORIZONTAL	the constant variable used to denote a horizontal scroll bar.
static int	VERTICAL	A constant that denotes a vertical scroll bar.

Inherited Fields

The Fields of AWT Scrollbar are inherited by:

• java.awt.Component
• java.awt.Adjustable
• java.awt.image.ImageObserver

Java AWT Scrollbar Methods

The followingreturn are the methods associated with the AWT Scrollbar class:

Method	Modifier and Type	Description
addAdjustmentListener(AdjustmentListener l)	void	Adds the specified adjustment listener to this scrollbar’s AdjustmentEvent instances.
addNotify()	void	used to instantiate a peer for the scrollbar.
getAccessibleContext()	AccessibleContext	Used to return the AccessibleContext for the scrollbar.
getAdjustmentListeners()	AdjustmentListener[]	Returns an array of all the adjustment listeners that have been registered on the scrollbar.
getBlockIncrement()	int	The scrollbar’s block increment is returned by this method.
getMaximum()	int	Gets the scrollbar’s maximum value.
getMinimum()	int	Gets the scrollbar’s minimum value.
getOrientation()	int	Returns the scrollbar’s orientation.
getUnitIncrement()	int	Returns the scrollbar’s unit increment.
getValue()	int	Returns this scrollbar’s current value.
getValueIsAdjusting()	bool	Detect any changes caused by used inputs it will return a true.
getVisibleAmount()	int	Obtains the scrollbar’s visible length.
paramString()	protected String	This method returns a string indicating the status of the scrollbar.
processAdjustmentEvent(AdjustmentEvent e)	protected void	Processes scrollbar adjustment events by sending them to any registered AdjustmentListener objects.
processEvent(AWTEvent e)	protected void	The events on this scrollbar are processed.
removeAdjustmentListener(AdjustmentListener l)	void	In order to prevent it from receiving instances of AdjustmentEvent from this scrollbar, the specified adjustment listener is removed.
setBlockIncrement(int v)	void	Controls this scrollbar’s block increment.
setMaximum(int newMaximum)	void	Sets the scrollbar’s maximum value.
setMinimum(int newMinimum)	void	Sets the scrollbar’s minimum value.
setOrientation(int orientation)	void	Sets the scrollbar’s orientation.
setUnitIncrement(int v)	void	Used to increase the size of scrollbar 1.
setValue(int newValue)	void	Sets this scrollbar’s value to the given value.
setValueIsAdjusting(boolean b)	void	Sets the valueIsAdjusting property.
setValues(int value, int visible, int minimum, int maximum)	void	Sets the values of four scrollbar properties: value, visibleAmount, minimum, and maximum.
setVisibleAmount(int newAmount)	void	Sets the visible amount of the scroll bar.

Inherited Methods

The Methods included with AWT Scrollbar are inherited by:

• java.awt.Component
• java.lang.Object

Examples of Java AWT Scrollbar

Now let us understand the Java AWT Scrollbar with the help of some examples along with their demo given below:

Example 1 (Basic Scrollbar):

In this example, two basic scrollbars are implemented. One is the default vertical scrollbar and the other is oriented horizontally. Their respective labels are also aligned below them for better understanding.

Below is the implementation of Java AWT Scrollbar:

Java

// Java code to implement basic
// Vertical and horizontal scrollbar
import java.awt.*;

// Driver Class
public class Main {
    // Main method
    public static void main(String[] args){

        // Create a frame
        Frame f = new Frame("Scrollbar Example");

        // Create a label and set its properties
        Label l = new Label("GeeksforGeeks");
        l.setBounds(130, 80, 200, 30);
        l.setFont(new Font("Arial", Font.BOLD, 20));
        l.setForeground(Color.GREEN);
        f.add(l);

        // Create a scrollbar (by default it is vertical)
        Scrollbar s1 = new Scrollbar();
        // Set the position
        s1.setBounds(280, 140, 40, 175);
        f.add(s1);

        // Create its respective label
        Label l1 = new Label("Vertical Scrollbar");
        l1.setBounds(260, 330, 200, 30);
        f.add(l1);

        // Create a horizontal scrollbar
        Scrollbar s2 = new Scrollbar(Scrollbar.HORIZONTAL);
        // Set the position
        s2.setBounds(50, 250, 175, 40);
        f.add(s2);

        // Create its respective label
        Label l2 = new Label("Horizontal Scrollbar");
        l2.setBounds(85, 330, 200, 30);
        f.add(l2);

        // Set the properties of the frame
        f.setSize(400, 400);
        f.setLayout(null);
        f.setVisible(true);
    }
}

Run the code using the following commands:

javac Main.java
java Main

Output:

Final Output of the Program:

Explanation of the above Program:

In the code snippet given above, we initialize a frame with a simple label titled “GeeksforGeeks”. Two scrollbars s1 and s2 are created. s1 is the default vertical scrollbar and s2 is set to be horizontal using the property Scrollbar.HORIZONTAL in the constructor. Both of them are added to a frame along with their appropriate labels, l1 and l2.

Example 2 (AdjustmentListener):

In Java AWT, adjustmentListener interface is used to handle the events triggered by scrollbars. It responds to the changes in the component’s value whenever the user interacts with it.

In this example, we have added adjustmentListener to both these scrollbars implemented in the above example. Whenever a user operates the scrollbar, the adjustmentValueChanged method is called and the respective labels are updated with their current values.

Below is the implementation of Java AWT Scrollbar:

Java

// Java code to implement scrollbar
// With adjustmentListener
import java.awt.*;
import java.awt.event.*;

// Driver Class
public class Main {
    // Main method
    public static void main(String[] args)
    {
        // Create a frame
        Frame f = new Frame("Scrollbar Example");
        // Create a label and set its properties
        Label l = new Label("GeeksforGeeks");
        l.setBounds(150, 80, 200, 30);
        l.setFont(new Font("Arial", Font.BOLD, 20));
        l.setForeground(Color.GREEN);
        f.add(l);

        // Create a scrollbar (by default it is vertical)
        Scrollbar s1 = new Scrollbar();
        // Set the position
        s1.setBounds(300, 140, 40, 175);
        f.add(s1);

        // Create its respective label
        Label l1 = new Label("Vertical Scrollbar");
        l1.setBounds(260, 330, 200, 30);
        f.add(l1);

        // Create a horizontal scrollbar
        Scrollbar s2 = new Scrollbar(Scrollbar.HORIZONTAL);
        // Set the position
        s2.setBounds(50, 250, 175, 40);
        f.add(s2);

        // Create its respective label
        Label l2 = new Label("Horizontal Scrollbar");
        l2.setBounds(65, 330, 200, 30);
        f.add(l2);

        // Add adjustment listener
        s1.addAdjustmentListener(new AdjustmentListener() {
            // Override the method
            public void adjustmentValueChanged(
                AdjustmentEvent e)
            {
                // Get the value of the scrollbar
                int val1 = s1.getValue();
                // Set the value of the label
                l1.setText("Vertical Scrollbar Value: "
                           + val1);
            }
        });

        // Do the same for the horizontal scrollbar
        s2.addAdjustmentListener(new AdjustmentListener() {
            public void adjustmentValueChanged(
                AdjustmentEvent e)
            {
                int val2 = s2.getValue();
                l2.setText("Horizontal Scrollbar Value: "
                           + val2);
            }
        });

        // Set the properties of the frame
        f.setSize(450, 450);
        f.setLayout(null);
        f.setVisible(true);
    }
}

Output:

Final Output of the Program:

Explanation of the above Program:

In the code example given above, a frame is initialized with a simple label and two scrollbars s1 and s2 as seen in the previous example. To both the scrollbars, we have added adjustmentListener to handle the events when the scrollbar is triggered. Inside the adjustmentListener, the adjustmentValueChanged method is overridden, which fetches the current value of the scrollbars. The updated value of these components is dynamically updated in the labels l1 and l2 as their value changes.