Wireless Java

A Simple Example

The examples that we’re going to demonstrate here, and throughout the rest of the book, are called MIDlets. If you’ve programmed with Java applets or servlets before, then you’ll likely recognize the similarities in the “fill-in-the-method” program structure. This first example, HelloMidlet.java, shown in Example 1-1, creates a text box and then prints the archetypal “Hello World” in a text box.

Example 1-1. “Hello World”

import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;

public class HelloMidlet extends MIDlet {

    // The display for this MIDlet
    private Display display;
    // TextBox to display text
    TextBox box = null;

    public HelloMidlet(  ) {
    }

    public void startApp(  ) {
        display = Display.getDisplay(this);
        box = new TextBox("Simple Example", "Hello World", 20, 0);
        display.setCurrent(box);
    }

    /**
     * Pause is a no-op since there are no background activities or
     * record stores that need to be closed.
     */
    public void pauseApp(  ) {
    }

    /**
     * Destroy must cleanup everything not handled by the garbage 
     * collector. In this case there is nothing to cleanup.
     */
    public void destroyApp(boolean unconditional) {
    }
}

This MIDlet consists of a public class definition that extends the MIDlet class found in javax.microedition.midlet . This superclass forms the base of all MIDlets in J2ME. Our HelloMidlet class contains a constructor, as well as the startApp() , pauseApp( ) , and destroyApp( ) methods that have been inherited from the MIDlet class. Note that there is no ...