Compiling Java with GCJ
Java bytecodes are a fairly direct encoding of Java programs not really designed for anything else. However, they have been used to encode programs written in other languages. See grunge.cs.tu-berlin.de/~tolk/vmlanguages.html for a list of other programming languages implemented on top of Java. Most of these are interpreters, but a few actually compile to bytecode. The former could use GCJ as is; the latter potentially can use GCJ to compile to native code.
One such compiler is Kawa, which I have been developing since 1996. Kawa is both a toolkit for implementing languages using Java and an implementation of the Scheme programming language. You can build and run Kawa using GCJ without needing any non-free software. The Kawa home page (www.gnu.org/software/kawa) has instructions for downloading and building Kawa with GCJ.
You can use Kawa in interactive mode. Here, we first define the factorial function and then call it:
$ kawa #|kawa:1|# (define (factorial x) #|(---:2|# (if (< x 2) x (* x (factorial (- x 1))))) #|kawa:3|# (factorial 30) 265252859812191058636308480000000
An interesting thing to note is the factorial function actually gets compiled by Kawa to bytecode and is immediately loaded as a new class. This process uses Java's ClassLoader mechanism to define a new class at runtime for a byte array containing the bytecodes for the class. The methods of the new class are interpreted by GCJ's bytecode interpreter.
Of course, it is usually more convenient to put the code in a file:
$ cat > factorial.scm (define (factorial x) (if (< x 2) x (* x (factorial (- x 1))))) (format #t "Factorial ~d is ~d.~%~!" 30 (factorial 30)) ^D $ kawa -f factorial.scm Factorial 30 is 265252859812191058636308480000000.
You can increase the performance of Scheme code by using Kawa to compile it ahead of time, creating one or more .class files:
$ kawa --main -C factorial.scm (compiling factorial.scm)You can then load the compiled file:
$ kawa -f factorial.class Factorial 30 is 265252859812191058636308480000000.To compile the class file to native code, you can use gckawa, a script that sets up appropriate environment variables (LD_LIBRARY_PATH and CLASSPATH) and calls gcj:
$ gckawa -o factorial --main=factorial -g -O factorial*.classUsing the wildcard in factorial*.class is not needed in this case, but it is a good idea in case Kawa needs to generate multiple .class files.
Then, you can execute the resulting factorial program, which is a normal GNU/Linux ELF executable. It links with the shared libraries libgcj.so (the GCJ runtime library) and libkawa.so (the Kawa runtime library).
The same approach can be used for other languages. For example, I am currently working on implementing XQuery, W3C's new XML-query language, using Kawa.
Other applications that have been built with GCJ include Apache modules, GNU-Paperclips and Jigsaw.
GCJ has seen a lot of activity recently and is a solid platform for many tasks. We hope that you consider Java for your free software project, using GCJ as your preferred Java implementation and that some of you will help make GCJ even better.
|Making Linux and Android Get Along (It's Not as Hard as It Sounds)||May 16, 2013|
|Drupal Is a Framework: Why Everyone Needs to Understand This||May 15, 2013|
|Home, My Backup Data Center||May 13, 2013|
|Non-Linux FOSS: Seashore||May 10, 2013|
|Trying to Tame the Tablet||May 08, 2013|
|Dart: a New Web Programming Experience||May 07, 2013|
- RSS Feeds
- Making Linux and Android Get Along (It's Not as Hard as It Sounds)
- New Products
- Drupal Is a Framework: Why Everyone Needs to Understand This
- A Topic for Discussion - Open Source Feature-Richness?
- Home, My Backup Data Center
- Validate an E-Mail Address with PHP, the Right Way
- New Products
- Tech Tip: Really Simple HTTP Server with Python
- Developer Poll
- git-annex assistant
43 min 34 sec ago
- direct cable connection
1 hour 6 min ago
- Agreed on AirDroid. With my
1 hour 16 min ago
- I just learned this
1 hour 20 min ago
1 hour 50 min ago
- not living upto the mobile revolution
4 hours 41 min ago
- Deceptive Advertising and
5 hours 17 min ago
- Let\'s declare that you have
5 hours 18 min ago
- Alterations in Contest Due
5 hours 19 min ago
- At a numbers mindset, your
5 hours 20 min ago
Enter to Win an Adafruit Prototyping Pi Plate Kit for Raspberry Pi
It's Raspberry Pi month at Linux Journal. Each week in May, Adafruit will be giving away a Pi-related prize to a lucky, randomly drawn LJ reader. Winners will be announced weekly.
Fill out the fields below to enter to win this week's prize-- a Prototyping Pi Plate Kit for Raspberry Pi.
Congratulations to our winners so far:
- 5-8-13, Pi Starter Pack: Jack Davis
- 5-15-13, Pi Model B 512MB RAM: Patrick Dunn
- Next winner announced on 5-21-13!
Free Webinar: Linux Backup and Recovery
Most companies incorporate backup procedures for critical data, which can be restored quickly if a loss occurs. However, fewer companies are prepared for catastrophic system failures, in which they lose all data, the entire operating system, applications, settings, patches and more, reducing their system(s) to “bare metal.” After all, before data can be restored to a system, there must be a system to restore it to.
In this one hour webinar, learn how to enhance your existing backup strategies for better disaster recovery preparedness using Storix System Backup Administrator (SBAdmin), a highly flexible bare-metal recovery solution for UNIX and Linux systems.