Java 2 Platform Micro Edition J 2 ME

Java 2 Platform, Micro Edition (J 2 ME) Masha Gutkhen Keren Gazit J 2 ME 1

Contents What’s J 2 ME? l J 2 ME core concepts l l l Configurations (CLDC, CDC) Profiles (MIDP) l MIDlet, MIDlet Suite l Basic classes API l Installation and using the Toolkit l Demos!!! J 2 ME 2

Introduction Personalized and intelligent information appliances are necessities in our life today. l Such appliances can be: l l l l cell phones two-way pagers smart cards personal organizers palmtops These appliances tend to be special-purpose, limited -resource, network-connected devices. J 2 ME 3

Environment requirements We need an environment which is adapted for constrained devices - devices that have limitations on what they can do when compared to standard desktop or server computers. l The constraints are: l l l extremely limited memory small screen sizes alternative input methods slow processors J 2 ME 4

So – what’s the solution? l Because of the vast need, Sun has decided to develop a special edition of Java - J 2 ME (Java 2 Micro Edition). J 2 ME 5

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Java Editions l Different devices have different requirements and different expectations of Java. l One platform (solution) cannot address all the market segments (web server, video games etc. ) l Users/developers want flexibility. They want to choose what they want to use and what they do not. J 2 ME 7

Java Editions l The Java 2 Platform is split into three editions. l Each edition provides a complete environment for running Java-based applications, including the Java virtual machine (VM) and runtime classes. l The three editions target different kinds of applications running on different kinds of devices. J 2 ME 8

Java Editions Java 2 Platform Java 2 Standard Edition (J 2 SE™) Java 2 Enterprise Edition (J 2 EE™) Java 2 Micro Edition (J 2 ME™) Standard desktop & workstation applications Heavy duty server systems Small & memory constrained devices J 2 ME 9

Java Editions Each edition defines different sets of class libraries. l There are thousands of core J 2 SE runtime classes, taking up to 10 -20 megabytes of space. J 2 EE l J 2 ME-based devices have J 2 SE fewer classes. l J 2 ME 10

Personal. Java and Embedded. Java l J 2 ME is not the first attempt at adapting Java for constrained environments. l Personal. Java Uses the basic Java 1. 1 runtime classes with a few features from Java 2. l Implementation still requires a couple of megabytes of memory and a fast processor to run. l J 2 ME 11

Personal. Java and Embedded. Java l Embedded. Java Makes every behavior of the JVM and the runtime classes optional - the implementor can choose exactly which classes and methods are required. l The limitation: "write once, run anywhere". l J 2 ME 12

Configuration l l Minimum platform required for a group of devices J 2 ME Libraries Profile l l J 2 ME Profile Addresses specific needs of a certain device family Java Language Java Virtual Machine Configuration l Profiles J 2 ME Core Concepts Optional Packages Host Operating System J 2 ME 13

J 2 ME Core Concepts J 2 ME is based on 3 core concepts: l Configurations l Profiles l Optional packages J 2 ME 14

Configurations l. A configuration is a complete Java runtime environment, consisting of: Java virtual machine (VM) to execute Java bytecode l Native code to interface to the underlying system l Set of core Java runtime classes l l To use a configuration, a device must meet certain minimum requirements. J 2 ME 15

Configurations l The set of core classes is normally quite small and must be enhanced with additional classes supplied by J 2 ME profiles or by configuration implementor. l Configurations do not define any user interface classes. J 2 ME 16

Configurations Configuration CLDC Connected Limited Device Configuration Connected Device Configuration J 2 ME 17

CLDC vs. CDC l CLDC l For very constrained devices l 160 - 512 KB of total memory l 16 -bit or 32 -bit processor l Low power consumption and often operating with battery power l Connectivity with limited bandwidth l J 2 ME CDC l 2 MB or more memory for Java platform l 32 -bit processor l High bandwidth network connection, most often using TCP/IP 18

CLDC vs. CDC - VM l Features missing in the CLDC VM: l l l l Floating point types Object finalization JNI or reflection Thread groups or daemon threads User Class loaders The CDC supports a complete, fullfeatured Java 2 virtual machine Change in classfile verification preverification J 2 ME 19

The KVM and CVM KVM - Java virtual machines for the CLDC l CVM - Java virtual machines for the CDC l Written specifically to work in the constrained environment of a handheld or embedded device and to be easily ported to different platforms. l CLDC and CDC specifications do not require the use of the KVM or the CVM. l J 2 ME 20

CLDC vs. CDC – J 2 SE Subset l The CLDC includes classes from: l l java. lang java. io java. util The CDC includes 17 packages l Includes more classes even in the shared packages l Only selected classes from each package are included J 2 ME 21

CLDC vs. CDC – J 2 SE Subset J 2 SE CDC J 2 ME CLDC 22

Handling I/O l J 2 SE includes many classes for performing input and output. l There a large number of I/O classes and they tend to encapsulate I/O models that are not necessarily found on all devices. l For example, some handheld devices do not have file systems. Socket support is not universal, either. J 2 ME 23

Handling I/O in CLDC The CLDC has define a new set of APIs for I/O called the Generic Connection Framework. l The GCF, part of the new javax. microedition. io package, defines interfaces for the different kinds of I/O that are possible. l The CLDC does not actually define any I/O implementations these are left to the profiles and/or the device vendor to define. l J 2 ME 24

GCF - example import java. io. *; import javax. microedition. io. *; Stream. Connection conn = null; Input. Stream is = null; String url = "socket: //somewhere. com: 8909"; try { conn = (Stream. Connection) Connector. open( url ); is = conn. open. Input. Stream(); . . // etc. }… J 2 ME 25

Handling I/O in CDC l Since the CDC is a superset of the CLDC, it includes the GCF. l CDC also requires GCF support for two specific connection types: files and datagrams. l The reason: CDC includes the relevant classes from java. io and java. net packages. J 2 ME 26

J 2 ME Core Concepts J 2 ME is based on 3 core concepts: l Configurations l Profiles l Optional packages J 2 ME 27

Profiles l Adds domain-specific classes to a configuration: l l To fill in missing functionality To support specific uses of a device Most profiles define user interface classes for building interactive applications. l To use a profile, the device must meet the minimum requirements of the underlying configuration and of the profile. l J 2 ME 28

Profiles Profile MIDP Mobile Information Device Profile PDAP Personal Digital Assistant Profile FP Foundation Profile J 2 ME PBP PP Personal Basis Profile Personal Profile 29

MIDP – MID Profile l MIDP is targeted at a class of devices known as mobile information devices (MIDs). l Minimal characteristics of MIDs: Enough memory to run MIDP applications l Display of at least 96 X 56 pixels, either monochrome or color l A keypad, keyboard, or touch screen l Two-way wireless networking capability l J 2 ME 30

MIDP - Specification l There are two versions of the MIDP: l MIDP 1. 0 - released in September 2000. Many devices currently on the market support it. l MIDP 2. 0 - currently in proposed final draft form. No devices yet support it. J 2 ME 31

MIDP - Specification l The MIDP adds APIs to the basic APIs defined by the CLDC. The new features include: l l Support for application lifecycle management similar to the way applets are defined in J 2 SE. Persistent storage of data. HTTP-based network connectivity based on the CLDC's GCF. Simple user interface support, with enough flexibility to build games or business applications. J 2 ME 32

MIDP - Specification l The MIDP specification is silent about a number of things: No standard way to interface to the device's phonebook, in order to initiate voice calls. l How MIDP applications are loaded onto a device and how they are activated or deactivated. l J 2 ME 33

MIDP Applications restrictions l Memory is a particularly scarce resource. l The early Motorola J 2 ME-enabled phones limited the size of an application to 50 K. Some Nokia phones limit them to even less, about 30 K. MIDP 1. 0 applications cannot share classes. l Placing part of the application in a web or application server (as a servlet, typically) that the MIDP application calls is almost a requirement for anything serious. l J 2 ME 34

J 2 ME Core Concepts J 2 ME is based on 3 core concepts: l Configurations l Profiles l Optional packages J 2 ME 35

Optional Packages l Set of APIs in support of additional, common behaviors. l Have specific dependencies on a particular configuration and/or one or more profiles. l Examples of optional packages : RMI Optional Package l Bluetooth Optional Package l JDBC Optional Package l J 2 ME 36

What it all means "J 2 ME application" is an ambiguous term. l Configuration, profile and optional packages should be chosen. l CDC-based profiles make development simpler due to J 2 SE-like APIs, but don’t suit the low-end devices. l CLDC-based profiles makes the development task harder, especially when trying to shrink the size of the application to run on many of the small devices. l J 2 ME 37

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MIDlets – The heart of J 2 ME… l MIDP does not support the running of applications that use a static main method as their entry point, nor calling the System. exit method in order to terminate. l Instead, we use a MIDlet, which is a MID Profile application. J 2 ME 39

MIDlets – The heart of J 2 ME… l Every application must extend javax. microedition. midlet. MIDlet class to allow the application management software to: control the MIDlet l be able to retrieve properties from the application descriptor l notify and request state changes l J 2 ME 40

MIDlets – The heart of J 2 ME… l The extending class is the main class of the application. l The MIDlet class defines abstract methods that the main class implements (for example: start. App(), destroy. App(), notify. Destroyed()). J 2 ME 41

MIDlet Suite l One or more MIDlets are packaged together into a MIDlet suite, composed of: JAR (Java archive) file l JAD (Java Application Descriptor) file l l All the user-defined classes and resources required by the suite's MIDlets must be in the JAR file. J 2 ME 42

MIDlet Suite l The JAR file must also include a manifest that describe the MIDlets in the suite. l The application descriptor (JAD) contains similar information, and is used by devices to obtain information about a MIDlet suite without having to download and install the MIDlet suite first. J 2 ME 43

Creating a MIDlet J 2 ME 44

Creating a MIDlet Importing MIDP specific packages import javax. microedition. lcdui. *; import javax. microedition. midlet. *; J 2 ME 45

Creating a MIDlet Extends MIDlet Implements Command. Listener public class Hello. MIDlet extends MIDlet implements Command. Listener { J 2 ME 46

Creating a MIDlet Creating the form, adding the Commands public Hello. MIDlet() { m. Main. Form = new Form("Hello. MIDlet"); m. Main. Form. append(new String. Item(null, "Hello, Seminar Software Design!")); m. Main. Form. add. Command(new Command("Exit", Command. EXIT, 0)); m. Main. Form. set. Command. Listener(this); } J 2 ME 47

Sample MIDP classes API l MIDlet l Form l Command. Listener l Item. Command. Listener l l Item J 2 ME 48

Sample classes API l MIDlet – Base class l Form l Command. Listener l Item. Command. Listener l l Item J 2 ME 49

MIDlet class API l l l protected abstract void start. App() protected abstract void pause. App() protected abstract void destroy. App(boolean unconditional) public final String get. App. Property(String key) public final void notify. Destroyed() J 2 ME 50

Sample classes API l MIDlet l Form l Command. Listener l Item. Command. Listener l l Item J 2 ME 51

Form class A Form is a Screen that contains an arbitrary mixture of items: images, read-only text fields, editable date fields, gauges, choice groups, and custom items. l In general, any subclass of the Item class may be contained within a form. l The implementation handles layout, traversal, and scrolling. l J 2 ME 52

Form class API l Item management l public int append(Item item) l public Item get(int item. Num) l Layout l public void set. Item. State. Listener(Item. State Listener i. Listener) J 2 ME 53

Sample classes API l MIDlet l Form l Command. Listener l Item. Commad. Listener l Item J 2 ME 54

Command class The Command class represents the semantic meaning of an action. Command objects are presented in the user interface. l The action itself is implemented in a Command. Listener object. l The Command. Listener is associated with a Displayable or an Item. l Once the Command is called – the Command. Listener is invoked, and the action is performed. l J 2 ME 55

Command class l Command label l public String get. Label() l Command type l public int get. Command. Type() l Command priority l public int get. Priority() J 2 ME 56

Command. Listener class API l This object is a listener for Commands that are attached to a Displayable. l public void command. Action(Command c, Displayable d) J 2 ME 57

Item. Command. Listener class API l When a command (attached to an Item) is invoked, the application is notified by having the command. Action() method called on the Item. Command. Listener that had been set on the Item. l public void command. Action(Command c, Item item) J 2 ME 58

Sample classes API l MIDlet l Form l Command. Listener l Item. Command. Listener l l Item J 2 ME 59

Item class l. A superclass for components that can be added to a Form. l All Item objects have a label field l Choose the Item’s layout, size, and appearance l Attach Commands J 2 ME 60

Item class API l public void set. Default. Command(Command cmd) l public void set. Item. Command. Listener(Item. Com mand. Listener listener) l public void notify. State. Changed() l public int get. Preferred. Width() J 2 ME 61

Getting Started… l 1 st step: Download sun’s J 2 ME Wireless Toolkit from: http: //java. sun. com/products/j 2 mewtoolkit/d ownload-2_1. html l 2 nd step: Make sure you have J 2 SE SDK installed l 3 rd step: Install the J 2 ME Toolkit. J 2 ME 62

After the installation…. l Shortcuts are available from the start menu. l New directories created J 2 ME 63

Using KToolbar J 2 ME 64

Creating a new Application Press “New Project”. l Enter the project’s name and the MIDlet’s class name. l New directories will automatically be created. l J 2 ME 65

Where to place your files? J 2 ME/apps/{proj}/bin J 2 ME/apps/{proj}/lib source, resource, and binary files JAR, JAD, unpacked manifest files. J 2 ME/apps/{proj}/res external class libraries, (JAR or ZIP) for a specific project resource files J 2 ME/apps/{proj}/src source files J 2 ME/apps/lib external class libraries, (JAR or ZIP) for all KToolbar projects. J 2 ME 66

And then what? l l l Choose the target platform JTWI - conforms to Java Technology for the Wireless Write your code Industry (JSR-185). Save MIDP 1. 0 - includes MIDP 1. 0 and CLDC 1. 0 Custom - user defined settings, you can select project Build profile, configurations and various APIs. (Compile + Preverify) Run J 2 ME 67

Distribution to actual devices l Create a package l Place your code somewhere on the net. l Update. jad file l Download the application to your mobile l Start playing… J 2 ME 68

Some other issues l OTA provisioning l Using Servlets l Working with Eclipse. ME l Web services J 2 ME 69

The END! l You can download all the demos JARs from: www. cs. huji. ac. il/~kerengaz/j 2 me/ l Have Fun!!! J 2 ME 70