Scrolling Text Box

import greenfoot.*;
import java.awt.Color;

// objects of this class will have text scroll within a textbox from right to left
public class Marquee extends Actor
{
    private GreenfootImage baseImg, textImg;
    private int scrollAmt;

    public Marquee(String text)
    {
        baseImg = new GreenfootImage(100, 20);
        baseImg.drawRect(0, 0, 99, 19);
        setText(text);
        updateImage();
    }

    // allows setting/changing of scrolling text
    public void setText(String text)
    {
        GreenfootImage stringImg = new GreenfootImage(text, 16, Color.black, new Color(0, 0, 0, 0));
        textImg = new GreenfootImage(stringImg.getWidth(), 20);
        textImg.drawImage(stringImg, 0, 10-stringImg.getHeight()/2);
        scrollAmt = baseImg.getWidth(); // reset scroller
    }

    // creates the image to display at current scroll position
    private void updateImage()
    {
        GreenfootImage image = new GreenfootImage(baseImg);
        image.drawImage(textImg, scrollAmt, 0);
        setImage(image);
    }

    // runs the scrolling of the text
    public void act()
    {
        scrollAmt--;
        if (scrollAmt ==-textImg.getWidth()) scrollAmt = baseImg.getWidth();
        updateImage();
    }
}