rjava

RJava enables Ruby to use Java classes in ruby programs using ruby-like syntax.

License

Probably LGPL or GPL.

Requirements

• J2SE 1.4.0 SDK or compatible (java.sun.com)
• Ruby 1.8.0 or compatible (www.ruby-lang.org)

Download

• rjava-preview-2003-10-19.tar.gz

Examples

Hello World!

This simple program lets the JVM print "Hello World!" on its console window.

require "java"

include JAVA

JVM.start_tcp().import("java.lang.System").out.println("Hello World!")

JFrame

require "java"

include JAVA

def create_pane
	pane = @jvm.new("javax.swing.JPanel", @jvm.new("java.awt.GridBagLayout"))
	gbc = @jvm.new("java.awt.GridBagConstraints")
	label = @jvm.new("javax.swing.JLabel", "Some Text")
	gbc.fill = gbc.jclass.BOTH
	pane.add(label, gbc)
	pane
end

@jvm = JVM.start_tcp
jframe_class = @jvm.import("javax.swing.JFrame")
jframe = jframe_class.new("Ruby-Swing-Sample")
jframe.setSize(300, 200)
jframe.setDefaultCloseOperation(jframe_class.DISPOSE_ON_CLOSE)
jframe.setContentPane(create_pane)
jframe.setVisible(true)

Limitations

The current implementation is an early preview with several limitations:

• The only supported communication channel between Java and Ruby is TCP/IP. Other channels using a pipe or JNI are planned for future releases.
• The communication is one-way from Ruby to Java. The next major release will allow call-backs from Java to Ruby by implementing Java interfaces with ruby classes.
• The Java objects that were referenced by ruby are never collected by the Java garbage collector. This will be fixed in the next major release.
• Tests, samples and documentation have to be added.
• Performance has to be optimized.

Background

The idea for this project was born during the First European Ruby Conference in Karlsruhe (Germany) on June 21th - 22th. I do the development in my spare time when my wife and my new born son let me do. Therefore my progress is very slow.

Contact

For installation problems, critique and suggestions please feel free to send me an email at rjava@spricom.com. Due to lack of time, I might not be able to answer each mail individually.

Author