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2.4 Java using barcode printing for applet control to generate, create datamatrix 2d barcode image in applet applications. barcode main class awt gs1 datamatrix barcode that the J2ME application developers must familiarize themselves with is the connector class. J2SE networking facilities assume the availability of a TCP/IP connection. Obviously, this assumption is not a valid one for mobile applications as a variety of communication protocols and schemes may be used to allow the device to communicate with the network.

So, CLDC de nes a connection framework in its Java API, providing a method for various network providers, device manufacturers, and protocol designers to offer the application developers options other than TCP/IP for communicating with the network. For example, it is possible that a vendor provides WAP-style connections (WDP/UDP) that can be invoked by CLDC connection objects by passing the right parameters to it. An example could be the following:.

Connection c = Connector.open("http://www.cienecs.

com");. As we menti Data Matrix barcode for Java oned previously, MIDP builds on the top of CLDC to offer the functionality required to build a real application. Let us review the MIDP APIs quickly. 1.

Timers: Two classes, java.util.Timer and java.

util.TimerTask, allow developers to write MIDlets that are started, one time or at some speci ed interval, at a given time. 2.

Networking: Whereas CLDC provides a generic connection framework that can be built upon by the device manufacturers and network providers, MIDP provides HTTP implementation, a high-level application networking protocol, that hides the lower layer implementation of networking between the device and the network (TCP/IP, WAP, etc.). The javax.

microedition.io. package holds the lone class of HttpConnection that allows connecting to network resources through HTTP.

3. Storage: javax.microedition.

rms. (where rms stands for record management system) provides a very simple API for storing and retrieving data. The query capabilities provided by this package, though extremely rudimentary, are invaluable as they provide the basics of database-like access to nonvolatile persistence on the device.

4. User Interface: javax.microedition.

lcdui. offers a set of rudimentary user interface APIs to build interfaces for MIDlets. Like the storage package, the user interface package is very simple.

However, it accomplishes much by offering an interface that is fairly generic, leaving the mapping of the interface to the implementation to the MIDP implementers. This increases the portability by allowing authoring of user interfaces without worrying about a great amount of detail on the implementation of MIDP on a particular device (though it still does not mean perfect portability). Now, let us look at a simple J2ME/CLDC application.

Hello MIDP CLDC applications only make sense as an application of a pro le. Because the user interface of the J2ME application is reserved for the pro les, writing a CLDC Hello. INTRODUCTION TO MOBILE DEVELOPMENT FRAMEWORKS World appli j2ee datamatrix 2d barcode cation really does not make that much sense. The pro le of choice for our example, obviously, will be MIDP. Applications for MIDs (Mobile Information Devices) are appropriately called MIDlets (like their counterparts of server-side applications, which are called servlets, small browser-based applications called applets, etc.

). As in applets and servlets, MIDlets are treated as components controlled by a framework under the inversion of the control principle to which we refer to frequently in this book. For a J2ME class to qualify as a MIDlet, it has to do the following: 1.

Extend the MIDlet class. 2. Implement the following methods: a.

startApp(): This method gets called after the class is instantiated. Think of this like the run() method of a thread in Java. b.

pauseApp(): This method is called if the application has to be suspended for some reason. Suspension of the application can be required for power saving, an incoming phone call, or a series of other reasons. c.

destroyApp(boolean b): This is used to do any maintenance necessary before the application is discarded. This method is necessary mainly because nalization and weak references are not available in J2ME. (It can be used for release of other resources as well depending on the type of the application.

) Figure 2.4 shows a simple MIDP application that simply shows a message on the screen and allows the user to exit the application. A variety of vendors, such as Borland and Sun, offer J2ME development tools.

Sun Microsystems has a free tool kit that offers the following components for development of J2ME applications: 1. KToolbar: This is the overtool that provides a GUI to manage collecting the classes that are put into the MIDlet, any name-value property sets that are used by the classes, and any resources such as icons used by the MIDlet. It also provides GUI control over build and bundling of the MIDlet into a deliverable package to the device.

2. Preveri er: As we mentioned previously, preveri cation of classes allows J2ME to of oad some work from the device. 3.

Compiler: The J2ME compiler compiles the classes. Remember that J2ME classes need to be preveri ed before they are ready to be used. 4.

Emulators: There is a series of emulators that ship with any development kit. Mobile device and mobile software vendors provide other emulators for J2ME. 5.

Emulation of Performance: The Preferences tool allows the developers to adjust for the virtual machine pro ciency, network performance, storage monitoring, and network traf c monitoring. These features have only been available in the latest version of the tool kit. Though they may seem secondary, they actually provide a huge leap over the previous versions of the tool as, for the rst time, some of the dimensions of mobility are treated within the tool kit.

These are namely limited devices resources and QOS..
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