09 display

Display

Cornelius Koo – 2005cornelius.mellino@gmail.com

What is Display

• The Display object working just like a

manager of the display controlling what is

shown on the device and when.

• javax.microedition.lcdui.Display

How to Get

• Display object is made available to MIDlet

through a call to static method declared

inside the Display class.

• The reference is often held for a lifetime of

MIDlet.

public class HelloWorld extends MIDlet {

private Display display;

public HelloWorld() {

super();

display = Display.getDisplay(this);

}

…

Display API

Example MIDlet : TestDisplay.java

Displayable

The Rules

• There is only one Display object per

MIDlet.

• Display object can show any number of

Displayable objects.

There are two class that extends Displayable. Those are

Canvas and Screen classes.

Creating Displayable Class

1. Extends Canvas class directly.

2. Use subclasses of Screen.

3. Extends from subclasses of Screen.

Extends Canvas Class Directly

public class MyOwnScreen extends Canvas

{

Drawing something…

}

Use Subclasses of Screen

TextBox t = new TextBox(

"Hello World MIDlet",

"Hello Small World", 256, 0);

...

display.setCurrent(t);

Extends From Subclasses of Screen

public class MyForm extends Form { }

Displayable API

Example MIDlet : TestDisplayable.java

Reference

• Core J2ME Technology and MIDP. John

W. Muchow. Prentice Hall PTR, 2002.

• Enterprise J2ME: Developing Mobile

Java Applications. Michael Juntao Yuan.

Prentice Hall PTR, 2003.

• J2ME in A Nutshell. Kim Topley. Oreilly,

2002.