You may ask why the scale factor is calculated in the paint() method rather than the init() method.
Some time could be saved by not recalculating the image's height
and width every time the image is painted. After all the image size
should be constant.
In this application the size of the image doesn't change, and
indeed it will be a rare Image that changes size in the middle of
an applet. However in the init() method the Image probably hasn't fully loaded. If instead you were to
try the program below, which does exactly that, you'd see that the
image wasn't scaled at all. The reason is that in this version the
image hasn't loaded when you make the calls to getWidth() and getHeight() so they both return
-1.
import java.applet.*;
import java.awt.*;
public class MagnifyImage extends Applet {
private Image theImage;
private int scaledWidth;
private int scaledHeight;
public void init() {
String filename = this.getParameter("imagefile");
theImage = this.getImage(this.getDocumentBase(), filename);
int scalefactor = Integer.parseInt(this.getParameter("scalefactor"));
int width = theImage.getWidth(this);
int height = theImage.getHeight(this);
scaledWidth = width * scalefactor;
scaledHeight = height * scalefactor;
}
public void paint (Graphics g) {
g.drawImage(theImage, 0, 0, scaledWidth, scaledHeight, this);
}
}