The Mobile Developer
by Eric Giguère
Java and Cellphones: The Motorola SDK for Java
Since my book
Micro Edition: Professional Developer's Guide is coming
out next month, I thought I'd spend a few columns
talking about Java and mobile devices. In this column
we tackle Java on cellphones, specifically looking
at the Motorola SDK for Java.
Why Java on Cellphones?
If your cellphone already supports WML or another markup
language (like HDML or Compact HTML), is there any
advantage to being able to run Java programs on it as well?
What can a Java program do that a set of WML decks
The first advantage is that Java is a proper programming
language, in the procedural/object-oriented sense,
and is used on a wide variety of platforms.
WML is a declarative language, to which you graft
some procedural logic using WMLScript, and is
used only on cellphones. Java is more suited for
complicated programming tasks.
The second advantage is that Java lets you work
offline. With a Java-enabled cellphone it's possible
to download and install an application that you can
then run without incurring connection charges,
something you can't really do when you're browsing
websites with the phone's microbrowser. You can
even run applications when you're out of coverage,
something that may be foreign to Europeans but something
that we North Americans -- with our vast geographical
areas and competing, incompatible networks -- have
to deal with on a regular basis.
Of course, you can work offline to a degree with WML
by using cached decks, but only if the decks are
designed to be cached. And you really don't have
much control over what gets cached, since it's all under
the control of the browser and the deck creator.
Java 2 Micro Edition
One of the problems with Java is that the runtime
system -- the Java interpreter, the native code
that interfaces to the operating system, and
the Java runtime library -- is quite large.
When I say "large", I mean several megabytes,
clearly too much for small computing devices
like today's cellphones. And that's where
Micro Edition (J2ME) comes in. Instead of merely
trimming fat from the Java 2 Standard Edition (J2SE),
J2ME is a complete rewrite of the Java runtime
with the specific memory and processing power
restraints of small devices in mind.
Central to J2ME are the concepts of
configurations and profiles.
A configuration defines the basic
features of a Java runtime system: what the
virtual machine must do, how much memory
is required, and the core set of runtime
classes (ideally a subset of ones in J2SE).
A profile builds on top of a configuration
(and even on top of other profiles) by
adding classes geared for a specific
family of devices or specific kinds of
There are currently two configurations
defined. The one that interests us
is the Connected Limited Device Configuration,
or CLDC for short,
which is optimized for cellphones and other
"limited" handheld devices. (To access
any of the specifications referred to in this
article, see the list of links I maintain
The CLDC defines a new virtual machine called the KVM,
and you'll often see people using the two terms interchangeably.
Unlike the "classic" VM included with J2SE, the KVM is
very memory-sensitive and is also easy to port to various
If you look closely at the CLDC, however, you'll see that it
only defines a very minimal set of runtime classes. In particular,
there are no user interface classes. This and other higher-level
functionality is left for the profiles to define. For the CLDC,
a profile called the Mobile Information Device Profile
has been defined which adds these basic features to the CLDC:
- application packaging and lifecycle ("MIDlets", similar to applets)
- user interface (both low-level and high-level)
- data persistence (simple record databases)
- network connectivity (HTTP support)
The expert group that defined the MIDP specification reads
like a "Who's who" of the handheld world, including
such leaders as Motorola, Nokia, Ericsson, Research in Motion,
Palm and others. So when phone and handheld manufacturers
talk about Java-enabling their devices, they're usually
referring to a MIDP-based J2ME implementation.
In fact, Motorola was the specification
lead for the MIDP, which brings us to the next topic....
Motorola's First Java-Enabled Cellphone
Motorola is set to release its first Java-enabled
cellphone this December, the i3000 (code-named
"Condor"), one of its family of multi-communication
devices that run on the iDEN (Integrated Digital Enhanced)
network (the major operators of iDEN networks
are Nextel in the US and Clearnet in Canada).
If you're unfamiliar with the technology behind iDEN,
a good summary and comparison to other technologies.
Although the i3000 is to be Motorola's first Java-enabled
phone, it won't be the last. Motorola has publically
committed to add Java support to all its new phone models,
not just the iDEN phones. Motorola has a large group
of developers working throughout the company on implementing
J2ME for its devices.
Developers anxious to try out an actual i3000 will have
to wait until the end of the year, but in the meantime
you can download Motorola's J2ME SDK from the
iDEN developer website.
You'll have to register, but it's free. As I write this,
the current SDK on the site is a beta, Developer Drop 5,
that complies with the MIDP 0.95 specification, so it's
slightly behind the MIDP 1.0 spec. Most of the functionality
is there, however.
Once you've downloaded the SDK, install it by extracting the
contents of the ZIP file into C:\MotoSDK. (You'll
need it there if you ever intend on using it with the
CodeWarrior for Java development tool from Motorola's
subsidiary, Metrowerks.) After installation, go to the
command line and run Motorola's cellphone simulator:
You'll see a simple MIDP sample running on your desktop
just like that in the screenshot accompanying this article.
This is one of several examples included with the SDK.
It also includes a very professional User's Guide
in PDF format that walks you through all the samples
and gets you started with some very basic MIDP programming.
You'll still need to get and read the actual MIDP specification,
of course, to do any serious programming.
Now that the MIDP 1.0 specification is final (it just happened
last month) and the i3000 is soon to be released, you can
expect to see an updated SDK show up soon with complete
support for the SDK. I know that I can hardly wait to get
my hands on an actual device!
More on J2ME programming next time...
Eric Giguère is the author of the upcoming
2 Micro Edition: Professional Developer's Guide and the
Database Programming: The Complete Developer's Guide.
He works as a developer for iAnywhere Solutions, a subsidiary of Sybase, Inc.
Visit his website at www.ericgiguere.com
or send him mail at email@example.com.