What is missing in J2ME?

[Mickey Segal]

Is there a detailed list of the functionality supported by J2ME for Windows
Mobile (Pocket PC)? Specifically, what would one need to change in the code
for a Java 1.1 applet to run it in the J2ME environment?

 

[Roedy Green]

Is there a detailed list of the functionality supported by J2ME for Windows
Mobile (Pocket PC)?

see http://mindprod.com/jgloss/j2me.html

I get the impression, you start from scratch with the gui part.

 

[Mickey Segal]

see http://mindprod.com/jgloss/j2me.html

I get the impression, you start from scratch with the gui part.

If J2ME really supports the Java 1.1 AWT, does a Java 1.1 applet need
re-writing? If Java 1.1 code did not need re-writing I'd imagine that lots
of people would be supporting the J2ME platform. However, that doesn't seem
to be the case, even though lots of applets on the Web are held at Java 1.1
to support MS JVM users. All the material I see on the Web about J2ME seems
vague, suggesting there is some problem, but it is not clear what the
problem is.

 

[Steven J Sobol]

If J2ME really supports the Java 1.1 AWT

It doesn't.

does a Java 1.1 applet need
re-writing?

It would.

If Java 1.1 code did not need re-writing I'd imagine that lots
of people would be supporting the J2ME platform. However, that doesn't seem
to be the case

Of course it's not. You can't fit the entire Java VM into a mobile device
with a minimal amount of memory.

even though lots of applets on the Web are held at Java 1.1
to support MS JVM users. All the material I see on the Web about J2ME seems
vague, suggesting there is some problem, but it is not clear what the
problem is.

J2ME seems to be really great for certain applications, but if you are
expecting to recreate an applet on a cell phone, you're likely to be
disappointed.

 

[Darryl L. Pierce]

Is there a detailed list of the functionality supported by J2ME for
Windows
Mobile (Pocket PC)? Specifically, what would one need to change in the
code for a Java 1.1 applet to run it in the J2ME environment?

You would need to rewrite the UI, persistent storage and networking classes
to use the LCDUI, RMS and GCF APIs that are available in the MIDP (assuming
you're going to use the MIDP implementation for PocketPC from IBM).

 

[Darryl L. Pierce]

If J2ME really supports the Java 1.1 AWT, does a Java 1.1 applet need
re-writing?

"J2ME" does not refer to any VM or API, it's only an umbrella term for all
smaller-than-desktop Java technologies.

Now, as for specific J2ME technologies:
o The MIDP does not support AWT, but instead has its own UI component set
called the LCUI; there is no commonality between AWT and LCDUI
o The Personal Profile uses a *subset* of AWT; there will be differences
that you will have to contend with.
o Neither use the same file IO APIs as Java 1.1; you will need to rewrite
that code.

If Java 1.1 code did not need re-writing I'd imagine that
lots
of people would be supporting the J2ME platform. However, that doesn't
seem to be the case, even though lots of applets on the Web are held at
Java 1.1
to support MS JVM users.

Applets are not a part of the J2ME technologies. You'll instead deal with
the similar-but-still-different MIDlet class.

All the material I see on the Web about J2ME
seems vague, suggesting there is some problem, but it is not clear what
the problem is.

Vague how? If anything, you might be reading material on the web by people
who are themselves unfamiliar with the J2ME technology family. The sources
I use (Sun and various printed sources, along with a few mailing lists) are
quite clear on the technology.

 

[Darryl L. Pierce]

It doesn't.

The Personal Profile (a J2ME technology) does. The MIDP doesn't.

 

[Darryl L. Pierce]

see http://mindprod.com/jgloss/j2me.html

Mate, your entry is wrong and misleading on several points:

o J2ME is not any single VM or set of APIs, but is an umbrella term
referring to a few different VMs with different minimum API sets, resource
requirements, etc. See the J2ME FAQ for some information on this subject
with real details

o No J2ME technology is a type of PersonalJava. The closest relative is the
Personal Profile which has a defined migration path for PersonalJava
applications but is not itself related to PJava.

o The VM you're referring to has being "2.5 meg and might be used in set top
boxes" is the CDC (Connected Device Configuration) and is not itself
anything more than a foundation on which the Personal Basis Profile (which
is itself designed for such things) is intended.

o The KVM is not designed for anything more than low powered networked
devices. The *MIDP* is intended for mobiles and lower-end PDAs, which the
Personal Profile is intended for more powerful PDAs such as the iPAQ.

 

[Steven J Sobol]

The Personal Profile (a J2ME technology) does. The MIDP doesn't.

MIDP would be what most cell phones use, and J2ME seems to me to be in widest
use on cell phones and cell/PDA combos.

 

[Roedy Green]

o The KVM is not designed for anything more than low powered networked
devices.

like what?

 

[Darryl L. Pierce]

like what?

Mobiles, watches, embedded devices with low powered CPUs and intermittent
network connectivity (MP3 player, electronics in a car dashboard, etc.).

 

[Darryl L. Pierce]

MIDP would be what most cell phones use, and J2ME seems to me to be in
widest use on cell phones and cell/PDA combos.

Yes, MIDP is mostly in use, although there are P(B)P devices and
implementations available now. However, you replied that "[J2ME] doesn't
[support AWT]" which is what I replied to. There *are* profiles under the
J2ME umbrella, such as Personal and Personal Basis Profiles, that *do*
provide the AWT. So, saying "[J2ME] doesn't [support AWT]" is wrong.

 

[Roedy Green]

Mate, your entry is wrong and misleading on several points:

I have made some corrections. Please check if I got it right.

See http://mindprod.com/jgloss/j2me.html

 

[Darryl L. Pierce]

I have made some corrections. Please check if I got it right.

See http://mindprod.com/jgloss/j2me.html

I would remove some of the sentences, such as:

"MIDP in common on pure cellphones."

What's a "pure cellphone"? I would just say that MIDP is what is found on
all mobiles listed as "Java-enabled".

"J2ME typically would be the Java language with the enterprise
communications stripped out of it (no remote RMI)."

This isn't exactly accurate. RMI is an optional package in J2ME.

"It would also have no security breakout."

Security's a big deal with the MIDP, more so than on the desktop. Newer
devices all but require MIDlet suites be signed, and most will not allow
either networking access without either digital signing or constant
approval from the user.

Otherwise, it's a good synopsis of J2ME

 

[Roedy Green]

"MIDP in common on pure cellphones."

What's a "pure cellphone"?

a cellphone that is not also a PDA.

 

[Mickey Segal]

I have made some corrections. Please check if I got it right.
See http://mindprod.com/jgloss/j2me.html

Thanks for helping sort this out. Someone was telling me that Java on
Windows Mobile was now so advanced that it ran regular Java and I didn't
know whether I had slept through something important or he had.

It is too bad. I was hoping he was right.