View source for DMelt:Programming/6 JRuby

= Using JRuby / Ruby =

You can program in [http://jruby.org/ JRuby language] JRuby as well.
Here are a few Ruby tutorials:

* [http://rubylearning.com/satishtalim/tutorial.html Ruby tutorial I]
* [http://www.troubleshooters.com/codecorn/ruby/basictutorial.htm Ruby tutorial II]

You can program in [http://jruby.org/ JRuby language] JRuby as well.
As usual, create a JRuby script in the editor (with the extension *.rb) and
run such scripts in the editor.
 
One important advantage of JRuby scripting is that programs (especially loops) in this language are faster then for Jython, and much faster than in BeanShell.
First, let us show how to make a standard Java JFrame:

<jcode lang="ruby">
include Java
import javax.swing.JFrame

frame = JFrame.new("Hello Swing")
button = javax.swing.JButton.new("Klick Me!")
button.add_action_listener do  evt 
  javax.swing.JOptionPane.showMessageDialog(nil, <<EOS)
<html>Hello from <b><u>JRuby</u></b>.<br>
Button '#{evt.getActionCommand()}' clicked.
EOS
end

# Add the button to the frame
frame.get_content_pane.add(button)

# Show frame
frame.set_default_close_operation(JFrame::EXIT_ON_CLOSE)
frame.pack
frame.visible = true
</jcode>

Save this file in "example.rb" and   run this script using the button  [[File:Run.png]] on the toolbar of DataMelt. 
One can also use the '''[F8]''' key for fast execution of a script. You will see a pop-up JFrame.
In case of an error, the DataMelt outputs error to bottom console. 



= JRuby and DataMelt =

Let us show how to work with scientific libraries using JRuby.

Let us rewrite Jython/Python example of how to create a histogram and shown it using 
[http://jruby.org/ JRuby language]. Our goal will be
to rewrite this script [man:data:histograms#plotting_a_histogram  showing H1D histogram].

First of all, one can use interactive JRubyShell of the IDE for prototyping and debugging. But our goal will be to write a script using the editor.

<jcode lang="ruby">
include_class Java::jhplot.HPlot
include_class Java::jhplot.H1D

c1=HPlot.new()
c1.setGTitle("Global labels: F_{2},  x_{&gamma;}  #bar{p}p F_{2}^{c#bar{c}}"); #put title
c1.visible()
c1.setAutoRange()

h1 = H1D.new("Simple1",100, -2, 2.0)
rand =java.util.Random.new()

print "Use of for loop in JRuby \n"
for i in 1..100
   puts "Value is => #{i}"
   h1.fill(rand.nextGaussian())
  end
c1.draw(h1)
</jcode>

Create a file  "example.rb" with this code (the extension "rb" is very important!)  and run this script as usual. 
To  run this script, use  the Run button  [[File::Run.png]] on the toolbar of DataMelt. One can also use the '''[F8]''' key for fast execution of a script.
In case of an error, the DataMelt outputs error to JRubyShell.

= Java class imports =


<ifauth !@member>
It should be noted that "java" is already imported automatically, i.e. no need to run the statement

<jcode lang="ruby">
require 'java'
</jcode>

as it is done automatically. 

Also, we import all jar files in lib/system directory. Check this using the statement

<jcode lang="python">
print $CLASSPATH
</jcode>

Finally, if you will need to import more jar files from some directory, use:

<jcode lang="ruby">
$CLASSPATH << "/jehep/lib/freehep"
Dir["/jehep/lib/freehep/*.jar"].each do  jar 
     print jar
     require jar
end
print $CLASSPATH
</jcode>

in this example we import all freehep jar files from the directory "/jehep/lib/freehep"

</ifauth>

[[Category:JRuby]]
[[Category:Dynamically typed programming languages]]
[[Category:Java programming language family]]
[[Category:Scripting languages]]