In the broad field of consumer electronics and embedded devices, the most attention is the mobile communication device, so it is necessary to introduce it.
The main operating system platform for mobile communication devices, which is important to the development of J2ME.
Mobile communication devices mainly include PDAs and smartphones, now there will be some devices in the border of PDA and smartphone now. Among them, the mobile phone market is much larger than PDA, so many foreign articles talk about J2ME are dominated by Wireless applications.
PDA is also handheld, generally refers to equipment such as Palm, which is similar to Palm, the main operating system.
Palm OS and
Pocket PC two major camps. Palm OS From Palm, it is an open system that dominates in the PDA market, and has a very much third-party manufacturer developed and a large number of very faithful and fanatical users. At present, Palm OS has the main Palm Series and Sony's CLIE series of Palm (Handspring's Visor), but has announced the exiting traditional PDA market, which mainly develops PDA and wireless communication-combined product Treo).
Pocket PC is launched by Microsoft and its partner Casio, Compaq, Hewlett Packard and Symbol,
Based on WIN CE 3.0, it is also an open standard system. The function can be extended unlimited to WIN CE is a closed unlatable system), which manufacturers can develop software on this platform. Specific products such as Compaq IPAQ.
In addition, Sharp Zaurus Series PDA uses Linux to a version of the embedded system. As a high-end PDA with up to 64M memory, you can meet the CDC standard, which is pre-installed with the Personal Java virtual machine.
In the field of smartphones, the main platform is Symbian's EPOC. EPOC is the first to develop Psion, mainly for smartphones, and PDA features, PSION is one of the first major PDA manufacturers. Psion announced that the first version of EPOC is open OS and authorizes other vendors. Subsequent PSION and Ericsson, Nokia, and later Motorola have established a league named "Symbian", the main shareholders are Motorola, Nokia, Panasonic , PSION and Sonyericsson, and Siemens April also announced. Symbian has a good foundation in Europe, using most major mobile phone manufacturers, typical products such as Norkia's 9210.
In these operating system platforms, there is already a reference implementation of MIDP on the Palm OS, but it is not the PROFILE that is best for PDA. Symbian implements CLDC and MIDP, as a smartphone operating system, is an ideal MIDP application platform. CDC (Pocket PC) has been implemented on the iPAQ of Compaq, and the previous mentioned, IBM WebSphere Micro Environment implements CLDC, CDC, and MIDP on the Pocket PC. Sharp's Zaurus implements Personal Java (Linux). Since these major operating system platforms are open, it can basically believe that the main mobile communication device operating system will always provide J2ME support, but which standard support does not necessarily define the original definition of CLDC and CDC, and The hardware conditions of the device are related to the selection of vendors, or multiple standards may be implemented.
Regarding the specific development of J2ME applications on mobile information devices, existing technologies are basically divided into the following categories:
Using early KVM and com.sun.kjava packs, or coupled with third-party KAWT libraries. There are many early articles and code, but this technology will be replaced by PDA profile, and does not guarantee compatibility, which is not recommended to use this method, but waiting for the final completion of PDA Profile and its implementation. Developed with CLDC and MIDP. Since the MIDP standard releases earlier, the smartphone is much more than PDA, this is the main content of a large number of wireless application articles, but its best goal is smartphones, although smartphones may have a certain PDA. Function, but this technology is not the most suitable for PDA.
With CDC and Personal Profile, such technologies are not very common, and the current mobile information equipment is still insufficient. But the next generation of PDAs and smartphones must be supported.
For the existing PDA hardware conditions, J2ME application is more difficult to compete with existing applications (for PDA):
Space: The general PALM class device memory is not equal from 2M to 16M (currently higher models already supports the expansion card, can be extended to 128M, but the speed of running the program on the card is much slower, generally mainly used Data, running programs can not depend on the card),
The standard size of the general existing program on PALM is less than dozens of k to 300k.
And only MIDP's Palm reference implementation is nearly 600K on Palm,
Plus as the foundation CLDC library, plus the program, it is about 1M. Compared with existing applications, there is currently no competitiveness.
Speed: Because Palm has always believed that "simple is beautiful" principle, the current Palm Series PDA mainly uses 33MHz Motorola 68000 series Dragonball, which brings cost reduction and power saving, but the performance of J2ME application It's hard to satisfy.
Function: PDA Profile, which is best for Palm, has not been completed, if it is developed with MIDP, it is not suitable, with early KVM and com.sun.kjava, because it is not J2ME standard, program compatibility cannot be guaranteed.
Nonetheless, the prospect of developing J2ME applications on mobile information devices is still very good:
Hardware Development: The current Palm is 8M to 16M memory is already mainstream, and the next generation of more than 32m is an inevitable trend.
Palm OS 5 finally started supporting 32-bit ARM RISC processors, and its speed should be able to increase 10 times. In fact, the Zaurus SL-5500 sold in the first quarter of this year has adopted Intel 206MHz Strongarm processors and 64M memory, and there is no problem in such hardware and memory.
The standard improvement: PDA Profile will finally completed this year, which can be expected to be achieved on major operating systems. There are also many other standards currently in JCP, such as Bluetooth, game, and positioning, etc.
The broadness of the platform: The main operating system platform of mobile information equipment is open, J2ME standard is also open, so basically all major operating system platforms support or will support J2ME, this brisk market (smart phone) The market is especially huge, but it is said that Norkia can ship 50 million Java mobile phones this year, and by 2003 can reach 100 million.) And real "once written, run everywelke" is any other technology unacceptable. For developers, it is not subject to the limitations of the operating system, and it doesn't have to worry about the changes in this changing market.
