J2ME JAVA

InputStream�� ByteArrayInputStream�� DataInputStreamOutputStream�� ByteArrayOutputStream�� DataOutputStream�� PrintStreamReader�� InputStreamReaderWriter�� OutputStreamWriter

CalendarDateHashTableRandomTimerTimerTaskTimeZoneVector�� Stack

MIDP Packages

javax.microedition.iojavax.microedition.lcdui (user interface)�� javax.microedition.lcdui.gamejavax.microedition.media (media player)�� javax.microedition.media.controljavax.microedition.midletjavax.microedition.pki (certification)javax.microedition.rms (persistence)

J2ME SDKs

Motorola SDK

RIM SDK

Java SDK

Competing Technologies

WAP/WML

I-Mode

Windows CE

Quick Start: "Hello World"

We will be using the Sun/Java J2ME SDK. This SDK includesthe J2ME Wireless Toolkit. Here"s its GUI (called K Toolbar):

Creating a New Project và Midlet

Applications that run on a MIDP/CLDC platform are called midlets.By pressing the "New Project" button we create a new project named Examplescontaining a midlet defined in a tệp tin named HelloWorld.class:

The console window informs us that it has created a projectdirectory named Examples containing src, res, and libsubdirectories:

Other subdirectories have been created as well. We must saveour .java files in the Examplessrc subdirectory.

HelloWorld.java

The tệp tin ExamplessrcHelloWorld.java is createdusing an ordinary text editor. It begins by importing several J2ME packages:

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

The declaration of the HelloWorld class follows:

J2ME APIs

HelloWorld extended the MIDlet class & contains referencesto a Display object (theDisplay) và a TextBox object (mainScreen). TextBoxextends the Screen class, which is the base class for all high-level GUIs.Low-level displays, where the programmer must define his own graphiyome.vn, extendthe Canvas class.

Typically, a midlet creates a collection of displayableobjects-- screens and/or canvases:

Displayable<> displayables = new Displayable;for (int i = 0; i �� // create displayables}

The midlet responds khổng lồ user input commands by selecting adisplayable object from this collection, then asking the display to display itwith the command:

theDisplay.setCurrent(displayables);

Here"s a more comprehensive class diagram showing the lcduipackage:

First notice that in addition to lớn text boxes, there are threeother types of screens: alerts (a message dialog that flashes on the display),forms (a control panel containing control items such as labels, text fields,and buttons), và lists.

A displayable can fire and handle commands. A command isfired when the user presses keypad buttons when the displayable is the currentwindow. When a command is fired, a command object is passed lớn thecommandAction() method of each registered command listener. Typically, themidlet is the command listener.

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Form items also fire commands. When an thành công command isfired, a command object is passed lớn the commandAction() method of eachregistered cống phẩm command listener. Typically, the midlet or the parent form isthe thành quả command listener.

The J2ME Application Manager

The Application manager manages the lifecycles of midlets:

Commands và The Midlet as a Command Processor

To demonstrate commands and command processing, let"s địa chỉ cửa hàng anew midlet lớn the Examples project. Pressing the Settings button on theWireless Toolkit toolbar displays the Settings dialog. Pressing the địa chỉ buttonat the bottom of this dialog allows us to add a new project called navigatorcontained in the CommandProcessor.class file:

Running the Command Processor

Here are some screen shots of the Navigator running on thesimulator. Notice that the opening screen now shows the Examples suite containstwo midlets. Selecting the navigator midlet causes the midlet"s first screen toappear. The screen is titled "Screen 0" và displays the question"Shall we go to lớn screen 1?". That"s all Navigator allows users khổng lồ do:to navigate from screen i to lớn screen j.

Notice that the phone"s soft buttons are labeled Backand Menu. The Back button will allow us to lớn return to lớn the midlet"sprevious screen. The thực đơn button displays a menu of commands the current screencan fire:

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Here"s what the thực đơn items do:

cmmd_0: displays anunimplemented warning screenOK: ���� displays suggested screen (screen1)Help: �� displays special helpscreen"Exit: �� terminates midletCancel:� Return to previous screen

Here are some shots of these other screens:

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CommandProcessor.java

The command processor midlet has much in common withHelloWorld. Instead of a single screen, the constructor will create an array offive screens plus a help screen. The startApp() method will displayscreen<0> in theDisplay.