Re: Java on the AS/400

** Reply to message from Vernon Hamberg <hambergv@goldengate.net> on Fri, 29
May 1998 16:23:46 -0500

> AFAIK, there's a HHHHHUUUUUGGGGEEEE difference between what MS has done and
> the classes provided by IBM.
> 
> The MS approach limits you to running a 'Java' app on a Windows platform.
> 
> The IBM approach does _not_ limit you to running on the 400. The
> applications that you create can run on any Java virtual machine. The
> 400-specificity here has nothing to do with Java. It's no different from
> using Lightning in VB to talk to the 400.
> 
> So, IMO, it's misleading to lump these approaches together, esp. to suggest
> that IBM is pulling the rug out from under the portability of Java by
> providing classes for 400 access.

Vernon, you are absolutely correct. 

In the case of Microsoft, what has happened is a modification to the Java
Virtual Machine. The JVM is the interface between the Java program and the
OS/hardware it is running on. For the concept of Java to work, the JVM must be
uniform on the "inside" where the programs access it. That way, Java programs
can make all the same calls no matter what machine it is running on. If you add
to, or delete from, the functions available in the JVM, you no longer have Java.

In the case of IBM, they have developed a set of classes for accessing AS/400
"native methods."

Native method calls are frowned upon by Java developers, because they access
methods which are specific to a platform. As an example, the emailer I am using
is a Java program. However, my web browser is Netscape. Netscape is not Java, so
for my emailer to execute my browser when I click on a link, it makes a "native
method call" and runs Netscape. The preferred method would be to call Java
browser and stay within the JVM.

Native method calls are standard within Java. There must be a way to access
native methods. What IBM has done is develop classes to make interaction with
some of the AS/400 native methods easy for developers.

What Microsoft has done is replace pieces of the Java Virtual Machine with
their own functions. These new functions replace items which are normally
standard. Like drawing a window or drawing graphics on a screen. Applications or
applets written to use these functions don't run on non-Windows machines. Then,
Microsoft decided to not include the normal Java version of these functions in
the Java Developer's Kit for Win32.


> Vernon Hamberg



Chris Rehm                                                    
Mr.AS400@ibm.net                                              
                                                              
How often can you afford to be unexpectedly out of business?  
Get an AS/400.                                                
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