Java Reference
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jf.setTitle("(" + jf.getX() + ", " + jf.getY() + ")");
But we cannot use the name jf because that variable name is not available
in method setTitleToOrigin . We need something more general, which can
refer to this instance, the object in which the method resides. Java uses the key-
word this for this purpose. So we put this statement in the body of
setTitleToOrigin :
this .setTitle("(" + this .getX() + ", " + this .getY() + ")");
Class OurFrame is in Fig. 1.8. Our sequence of statements now works!
OurFrame ourWindow= new OurFrame();;
Compile class ourFrame in your IDE and then experiment with it. After execut-
ing the above statements, drag the window to a different place on your monitor
and then execute the call to method setTitleToOrigin again.
The manila folder for an instance of class OurFrame
Earlier, we showed how to draw an instance of a class as a manila folder,
with the name of the folder in the tab, the name of the class in a box in the upper
right, and the methods and fields in the folder itself. Drawing a folder of class
OurFrame is slightly different because it extends class JFrame . An OurFrame
manila folder has to have all the methods and fields that a JFrame has plus those
that are defined in OurFrame .
We show a manila folder of class OurFrame in Fig. 1.9. The folder has two
partitions. The top partition shows all the methods and fields that an instance of
superclass JFrame has. The bottom partition has the methods and fields that are
defined in subclass OurFrame . Of course, all the methods in both partitions are
available for use.
It is easy to remember how to draw such a folder. The superclass partition is
at the top, and the subclass ( sub means under ) partition is underneath the super-
class partition.
import javax.swing.*;
public class OurFrame extends JFrame {
/** Set the title of this instance to contain the origin of the window */
public void setTitleToOrigin() {
this .setTitle("(" + this .getX() + ", " + this .getY() + ")");
Figure 1.8:
Class OurFrame , which is placed in file
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