NetRexx is the best computer programming language
available. You might
suspect that the writer is biased and you would be correct. However,
if you program for a little while in NetRexx, you may just end up with
the same bias! I say that after spending over 30 years programming in
COBOL, FORTRAN, various assembly languages, APL, BASIC, REXX, JCL,
CLIST, C, PERL, etc. Some NetRexx programmers I know have far more
language experience than mine.
This guide assumes that the reader has some familiarity with computer
programming and knows what computer languages
are, as well as why there
are compilers or translators
for those languages.
You may have heard
that NetRexx is "compatible" with the Java programming language or that
NetRexx is a "dialect" of Java or some similar statement. While there
is truth in those statements, they can also be misleading. This
document will try to clarify the relationship between NetRexx and Java
as well as giving an idea of what can be done with NetRexx.
If you want
to verify that the examples in this guide actually work, you will need
to first wade through the NetRexx installation document
to get a
minimal development environment running. An easier way to try things if
you are familiar with the "jEdit" file editing environment or have a
few minutes to try it, is to install the NetRexx plugin
jEdit Plugin menu and cut and paste the examples into that environment.
This document is not intended for experienced Java programmers. Those
readers should simply know that NetRexx is an alternative JVM language
like Groovy or JPython which can be used to produce Java source code, class files
or jar files, and take a look at this document comparing
NetRexx and Java syntax: NetRexx at Once
What is NetRexx?
In a practical sense, NetRexx is a completely unique language that just happens to be able to use any Java objects and to run
anywhere that Java can run. Under the hood, NetRexx code can be
converted into Java code by the NetRexx Translator and compiled to
create Java objects that are just like those produced by Java
programmers. But NetRexx code can also be directly interpreted as a
scripting language by the NetRexx Translator which runs in a Java
Virtual Machine (JVM).
With a suitable IDE, NetRexx code can even be
compiled to run in environments similar to the JVM such as the Dalvik
VM used on Android devices (like cellular phones and tablet computers) or the leJOS NXT VM for robots. NetRexx was
created by Mike Cowlishaw, at that time working for IBM, who
also wrote the primary NetRexx book ("The NetRexx Language") as well as
the NetRexx Translator.
Why use NetRexx?
The NetRexx language was inspired by the REXX programming language
follows the same principles. The main principle is that the language
should be easy for programmers to read and write without regard for how
difficult it might be for a computer to understand. For example, NetRexx
does not use unneeded special characters (like braces) to signal program structure to
the Translator as some other languages do.
What can you do with NetRexx?
The short answer is: Anything! More precisely, because NetRexx can
produce Java programs and run in most Java environments, you can do
anything with NetRexx that a Java programmer could do in Java. Can you
write GUI (graphical user interface) programs with NetRexx? Yes! Can
you write major applications in NetRexx? Yes! Can you write NetRexx
programs which call Java code? Yes - all of the Java classes and
objects in any Java libraries
available can be used by NetRexx programs.
What can you NOT do with NetRexx?
Not much. But you cannot directly mix Java source code with NetRexx
- they are different animals and the translators for each language will
choke if they see code from the other language. However, once Java code
and NetRexx code have been separately compiled into machine language
(JVM code), they can access each other with no problems.
Enough propaganda - show me
Every programming language intro is obligated to start with the traditional "Hello World" program so here it is in NetRexx:
say "Hello World"
OK, no big deal - lots of languages can do that program in one line.
But how many can do an Internet browser in one line? Here is one in
NetRexx (Pass a web address to this program):
Granted, that program is of limited use since it only tells you if a
web document exists but that is more than enough to do stress testing
or access verification for web sites, so it can be considered a
practical application and an interesting NetRexx example.
Some readers may be interested in examining the content of the web
document obtained above, so here is a program that will list the
document source code:
pagereader=BufferedReader(InputStreamReader(InputStream URL(arg).getcontent ))
if line = null then leave
Let's get graphical
Maybe you want to know how easy it is to do something more complex,
perhaps with a GUI interface. Try this program
(move your mouse pointer
in the window while pressing the mouse button):
class pencilapp extends Applet
x =int 0 ; y =int 0
method mouseDrag(e=event,i=int,j=int) public returns boolean -- if mouse is moved with button pressed, draw a matching line
x = i ; y = j
method mouseDown(e=event,i=int,j=int) public returns boolean -- when mouse button is pressed, record it's location
x = i ; y = j
method main(argv=String) public static -- if no Applet window is available, build a window frame and put this object in it
The above graphical drawing program can run all by itself or can be embedded in a web document.
What about Java library objects?
The examples above make use of various classes or objects from the Java
, such as
the URL class, the Applet class and the Frame class. Java items like
these can be used directly in NetRexx programs without doing anything
special because they are simply external objects to NetRexx. These
library objects (much like external functions) should not be considered
to be part of the Java language but simply as part of the virtual
machine environment that Java and NetRexx programs run in. (The
assumption here is that you have a valid Java environment
available to run programs in, of course.)
For example, the Java library documentation tells us that there is a
"Date" class which can be used to create a Date object for the current
object and initializes it so that
it represents the time at which it was allocated, measured to the
This Java object can be created and displayed as a string by NetRexx with the following statement:
In fact that one line is a complete NetRexx program that creates and
then displays a Java object in a text format . The NetRexx program
loads the Java library object at run time and calls it as needed. The
conclusion that you
should draw is that it is very easy to work with Java items from within
NetRexx. Often easier than it would be from Java itself.
A quick glossary
- A Computer Language
is a simplified set of commands and expressions that a human can write
a plan (program) with and a computer can then translate into binary
data that tells a computer what to do in some situation.
- A Compiler
or translator is a computer application which can recognize a computer
language and translate programs written in it into a simple format
which makes it easier for a computer to follow directions given in that
- A Class File is a list of computer instructions which has been compiled into a simple format which a computer can easily understand.
- A Computer Language Library
is a group of class files which tell a computer how to perform various
functions that may be needed by a computer application when something
is requested by a computer user.