Source

import java.applet.*;
import java.awt.*;
import java.awt.event.*;

public class AnAppletWithScrollbar extends Applet implements AdjustmentListener {
	public void init() {
		scrollbar = new Scrollbar(Scrollbar.HORIZONTAL, 50, 0, 0, 100);
		add(scrollbar);
		scrollbar.addAdjustmentListener(this);
		textField = new TextField(3);
		textField.setEditable(false);
		add(textField);
	}

	public void adjustmentValueChanged(AdjustmentEvent e) {
		textField.setText(scrollbar.getValue()+"");
	}

	Scrollbar scrollbar;
	TextField textField;
}

Notes

• A Scrollbar is an interface component that allows the user to easily move within a specified range of values
• The scrollbar may be manipulated
  • via the arrrows at either end
  • By dragging the 'thumb' (the little box in the scrollbar's gutter)
• At any point the value of the scrollbar may be retrieved/modified via the getValue, setValue methods

• As with buttons, the applet must register as a listener to the scroll bar
• In the case of the scroll bar, the event generated is known as an adjustment event and the applet registers as an AdjustmentListener.
• The event-handling method for scrollbar events is adjustmentValueChanged

This Applet's Behavior

• The init Method
  • A Scrollbar object is created and placed on the applet
    • horizontal
    • an initial value of 50
    • a minimum value of 0
    • a maximum value of 100
    • Note: for our purposes, always set the visible argument to the constructor to 0
  • The applet registers with the Scrollbar object as a listener
  • A TextField is created and placed on the applet
    • The applet will display the value of the scrollbar in the text field.
• The adjustmentValueChanged
  • When the user makes an adjustment of any sort to the scrollbar, this method is invoked
    • If mutliple scrollbar's are present, the getSource method can be used, just as in actionPerformed
  • In this applet, the method simply retrieves the (new) value of the scrollbar and puts it into the text field
    • Note that the integer value returned by getValue must be converted to a String

Things to Do

• The Scrollbar class
  • What package is it in?
  • What are the various constructor options?