Object-Oriented Introduction to Java - Multimedia Introduction to Programming Using Java - page 45

class-type String instead of keyword void . This type defines the type of the
variable that the function returns.
Functions are different from procedures in that they return a value. To state
what a function returns, use a return statement , of the form

return expression ;
Execution of the return statement evaluates the expression , stops execution
of the function body, and yields the value of the expression as the result of the
function call. In getPreviousTitle , the expression is this .previousTitle ,
and its value is the value in that field.

Drawing a folder that contains a field
Figure 1.11 contains an instance of the revised class OurFrame . We have
placed field previousTitle in it, as well as getter method getPreviousTitle .
Field previousTitle is grayed out to indicate that it is private , so it cannot be
referenced outside the class.

1.4.3 Self-review exercises

Hopefully, you have had your IDE open while you read Sec. 1.4 and have tried
making JFrame s. These exercises will give you more practice with JFrame s and
with writing customized window classes.

SR1. Type into Java this import statement:

import javax.swing.*;

import javax.swing.*;
public class OurFrame extends JFrame {

/** Class invariant: previousTitle contains the previous title (initially "" ) */
private String previousTitle= "";

/** Set the title of this instance to contain the origin of the window */
public void setTitleToOrigin() {
this .previousTitle= this .getTitle();
this .setTitle("(" + this .getX() + ", " + this .getY() + ")");

}

/**= the previous title (empty "" if none) */
public String getPreviousTitle() {
return this .previousTitle;

}

}
Figure 1.10: Class OurFrame , revised to maintain the previous title