Java for Mobile Phones and other Self-contained Devices
Anyone with programming skills can develop basic Java
applications for mobile phones, and for a very small startup cost, as you can
develop and test them on a PC using any of the free tools mentioned on these
pages, and then upload them to the phone from the PC, or download them
from your own web or WAP site, or e.g. via
GetJar. This is provided you give them away for free. If you intend to go commercial it gets a bit more complicated, especially if you intend to host your own e-commerce solution. There are
also e-commerce brokers (read: distributors) for mobile applications, e.g. ClickApps, yet they usually take a big chunk of the revenue. It also gets more complicated if you want your application to run
on many different phones. Functionality fragmentation is one of the big issues with Java ME, something the industry is well aware of,
but hasn't yet solved satisfactorily. The only viable solution to date is to test on every
supported phone and adapt, which can be very costly for smaller companies and individuals. There are though labs that focus on such testing and there are also frameworks (e.g.
J2ME Polish) that
make this less of a problem.
There are lots of applications you can download
for free or for a small fee, at this time primarily games, but increasingly also productivity and communication applications. If you have a great idea for a new application you can use e.g.
GetJar for checking if there's any chance you can provide something unique, and also "spy" on what others have done.
Talking about trends, it's very clear that online services (public and
corporate) will be complemented by Java ME applications in phones to provide a
better responsiveness, functionality and user interface than possible via browsers and
messaging clients. Most mobile phones now support Java ME CLDC/MIDP.
Java ME is an application platform using Java as a programming language,
initially intended
for smaller self-contained and possibly mobile devices like set-top boxes, PDAs, mobile phones
etc. Covered here is Java ME for specifically mobile phones, which in
practice means Connected Limited Device Configuration (CLDC) and Mobile Information Device Profile (MIDP). Java applications for mobile phones are called MIDlets,
reflecting they are MIDP compliant. A few smartphones are shipped with support for CDC as well, that's much closer to Java SE in functionality, but for the foreseeable future CLDC / MIDP will
rule. If you are completely lost now, see Terminology
for an explanation of the above.
It should be noted that
there are several combinations of MIDP versions, CLDC versions and optional
JSRs being used in mobile phones. Java Technology for the Wireless Industry (JTWI;
aimed at lowering the feature fragmentation) has been broadly adopted by the
industry, but there's a lot of crucial functionality not covered by JTWI, including advanced multimedia, MMS messaging, location etc. When counting all the
optional JSRs for Java ME it's a very feature-rich application platform indeed, but it's very much dependent on the phone model, and its age and overall functionality, what JSRs are actually supported.
MIDP defines a high level of security to minimize the risk of the user downloading applications that might be viruses or detrimental in other ways. That didn't stop e.g. the Russian "Red Browser"
that simply asked the user to select "Yes" on all permission warnings emitted by the phone, so the human factor can still override the security scheme. Anyway, there are two key reasons for why you
should sign your application, and that way get rid of permission warnings:
the signing is a stamp of approval that your company stands behind the application
the user experience can improve
considerably (of course depending on how much permission-controlled functionality you use)
If you provide your application to telecom operators they often take care of this for you. If you sell on
your own you need to buy a certificate from Thawte, Verisign or other similar provider. Of course, if your application doesn't generate any
or just a few permission warnings now, then signing won't make much difference,
and there's no such thing as a cover-all signing. You might have to sign the application several times for different operators and phone brands.
Almost all MIDlets available on the market are unsigned.
Note: Java ME was previously called J2ME as in "Java 2 Platform, Micro
Edition". Not even Sun itself has fully adapted to the new name yet.
