PDAP Programming - Java 2 Micro Edition Application Development - page 82

Chapter 4. PDAP Programming
IN THIS CHAPTER
• PDAP Application Life Cycle
• PDA User Interface
This chapter discusses the life cycle and user interface of PDA applications. First, we'll talk about
the general design of PDA applications. Then, we'll explain the AWT subset that forms the PDAP
user interface API.
PDAP Application Life Cycle
PDAP is a complete superset of MIDP. As for MIDP, PDAP applications are based on the MIDlet class
and share the MIDlet life cycle, as illustrated in Figure 3.1 . However, PDAP contains several additional
packages. For example, the AWT classes allow much more sophisticated user interfaces than lcdui,
giving the programmer fine-grained control over component layout.
In this chapter, we will concentrate on the user interface enhancements of PDAP.
HelloPdap Revisited
The HelloPdap example from Chapter 1 , "Java 2 Micro Edition Overview," is already a complete
PDAP application. Now that you have the necessary foundation, you can revisit HelloPdap from an
API point of view.
First, you import the necessary midlet and awt packages:
import java.awt.*;
import javax.microedition.midlet.*;
Like all PDAP applications, the HelloPdap example is required to extend the MIDlet class:
public class HelloPdap extends MIDlet {
In the constructor, you create a Frame titled "HelloPdap" :
Frame frame;
public HelloPdap() {
frame = new Frame ("HelloPdap");
}
You do not add content to the frame yet, so only the title will be displayed. (A description of the awt
classes is contained in the " PDA User Interface " section.)
When your MIDlet is started the first time or when the MIDlet resumes from a paused state, the
startApp() method is called by the program manager. Here, the show() method of the frame is
called, requesting that the frame be displayed. If the frame is already visible, it is brought to the
foreground: