jRuby: The best of both worlds

jRuby
The best of both worlds

Christopher Spring

Yukihiro “Matz” Matsumoto

“I wanted a scripting language that was more powerful
than Perl, and more object-oriented than Python...”

“[We] need to focus on humans, on how humans
care about doing programming... We are the masters.
They are the slaves.”

“I hope to see Ruby help every programmer in
the world be productive, and to enjoy
programming, and to be happy.
This is the primary purpose of Ruby language”

# booleans
truth = true
lies = false

# Strings
dude = 'Matz'
credo = "#{dude} is nice,
so we are nice!"

# Numbers
42 ** 13
53.8 / 9
19 % 3

# Arrays
backpack = [6, 'apple', [true, some_object]]

# Hashes
hash = {
true => 'He loves me!',
dude => 'Must obey!',
backpack => false
}

# symbols
cities = [:paris, :new_york, :johannesburg]

coders = [
{ 'language' => 'ruby', 'location' => 'johannesburg' },
{ 'language' => 'java', 'location' => 'port elizabeth' },
# ...
{ 'language' => 'ruby', 'location' => 'pretoria' }
]

# vs.

coders = [
{ :language => 'ruby', :location => 'johannesburg' },
{ :language => 'java', :location => 'port elizabeth' },
# ...
{ :language => 'ruby', :location => 'pretoria' }
]

public Class Person {
private String firstName, lastName;

public Person(String firstName, String lastName){
setFirstName(firstName);
setLastName(lastName);
}

public String getFirstName(){
return firstName;
}

public String getLastName(){
return lastName;
}

public String setFirstName(String firstName){
this.firstName = firstName;
}

public String setLastName(String lastName){
this.lastName = lastName;
}
}

class Person
attr_accessor :first_name, :last_name

def initialize(first_name, last_name)
@first_name = first_name
@last_name = last_name
end
end

class Person
attr_accessor :first_name, :last_name

@first_name = first_name
@last_name = last_name
end
end

person = Person.new( 'Nick', 'Cave')
person.first_name = 'Slick'
person.last_name = 'Nave'
puts "#{person.first_name} #{person.last_name}"

Btw, everything is an
Object!

true.class() # => TrueClass
false.to_s() # => "false"

5.9.floor() # => 5

3.times{ puts('Hello JUG!') }
# => Hello JUG!
# => Hello JUG!
# => Hello JUG!

module Earth
class Person
attr_reader :first_name, :last_name

@first_name, @last_name = first_name, last_name
end
end
end

module Earth
class Person
attr_reader :first_name, :last_name

@first_name, @last_name = first_name, last_name
end
end
end

chap = Earth::Person.new('Chandler', 'Bing')
chap.first_name # => Chandler

module RepublicPersonnel
def storm_trooper
Earth::Person.new('Storm', 'Trooper')
end
end

class CloningVat
extend RepublicPersonnel
end

module RepublicPersonnel
def storm_trooper
Earth::Person.new('Storm', 'Trooper')
end
end

class CloningVat
extend RepublicPersonnel
end

#<Earth::Person @last_name="Trooper", @first_name="Storm">
CloningVat.storm_trooper

module TehForce
def sense
'... a disturbance in the force'
end
end

module Earth
class Person
include TehForce
end
end

module TehForce
def sense
'... a disturbance in the force'
end
end

module Earth
class Person
include TehForce
end
end

farm_boy = Earth::Person.new('Luke', 'Skywalker')

# => '... a disturbance in the force'
farm_boy.sense

def some_days( something_happens )
puts 'The sun rises'
puts something_happens
puts 'The sun sets'
end

def other_days( this_happens, and_that_happens)
puts this_happens
puts and_that_happens
puts 'The sun sets'
end

some_days 'I do some work'
other_days 'I skip', 'I read a book'

puts 'The sun sets'
end

puts 'The sun sets'
end

def some_days
yield
puts 'The sun sets'
end

some_days { puts 'I go to work' }

some_days do
puts 'I skip'
puts 'I read a book'
end

file = File.open('i <3 ruby.txt', 'w')
file.puts "... i really do!"
file.close

file = File.open('i <3 ruby.txt', 'w')
file.close

File.open('i <3 ruby.txt', 'w') do |file|
end

Rubyists TATFT!
describe Calculator do
before(:each) do
@calc = Calculator.new
end

context 'Addition' do
it 'returns 10 when adding 5 and 5'
@calc.add(5,5).should == 10
end

it 'returns 0 when adding 5 and -5' do
@calc.add(5,-5).should == 0
end
end
# ...
end

class Person
def initialize
@height, @weight, @hair_color = 6.2, '70kg', 'brown'
end

%w(height weight hair).each do |property|
define_method("#{property}") do
i_var = self.instance_eval("@#{property}")
i_var.to_s.upcase
end
end

def method_missing(*args, &block)
puts "I dont have #{args[0].to_s.gsub(/_/, ' ')}"
end
end

p = Person.new
p.my_height # => 6.2
p.my_weight # => 70KG
p.my_hair_color # => BROWN
p.your_car_keys # => I dont have your car keys

Interactive Ruby

$ jirb
jruby-1.6.7 :001 > require 'java'
=> true
jruby-1.6.7 :001 > #...

class Ackermann
def self.ack(m, n)
return n + 1 if m.zero?
return ack(m - 1, 1) if n.zero?

ack( m - 1, ack(m, n - 1) )
end
end

include Rubeus::Swing

JFrame.new('Ackerizer') do |frame|
frame.layout = java.awt.FlowLayout.new
@m, @n = JTextField.new('3'),JTextField.new('10')

JButton.new('->') do
start = Time.now

@result.text = Ackermann.ack(
@m.text.to_i,
@n.text.to_i
).to_s

puts "#{Time.now - start}"
end

@result = JTextField.new 10

frame.pack
frame.show
end

class Ackermann
def self.ack(m, n)
return n + 1 if m.zero?
return ack(m - 1, 1) if n.zero?

ack( m - 1, ack(m, n - 1) )
end
end

public class Ackermann {
public static int ack(int m, int n) {
if (m == 0)
return n + 1;

if (n == 0)
return ack(m - 1, 1);

return ack(m - 1, ack(m, n - 1));
}
}

include Rubeus::Swing

JFrame.new('Ackerizer') do |frame|
frame.layout = java.awt.FlowLayout.new
@m, @n = JTextField.new('3'),JTextField.new('10')

JButton.new('->') do
start = Time.now

@result.text = Java::Ackermann.ack(
@m.text.to_i,
@n.text.to_i
).to_s

puts "#{Time.now - start}"
end

@result = JTextField.new 10

frame.pack
frame.show
end

Method overloading
public class OverloadTypeChecker {
public static String inspect(long value) {
return "long";
}

public static String inspect(String value) {
return "string";
}

public static String inspect(Object value) {
return "object";
}
}

require 'java'

java_import 'OverloadTypeChecker' do
'OTC'
end

# jRuby happily handles the simple case
OTC.inspect(5) # long
OTC.inspect('Helloooo!') # string
OTC.inspect([]) # object

public class BitLength {
public int neededFor(int i) {
return 32;
}

public int neededFor(long l) {
return 64;
}
}

# jRuby can be forced to use a specific overload
require 'java'
java_import 'BitLength'

bits = BitLength.new
bits.needed_for(1_000_000) # 64

require 'java'


# java_send
bits.java_send :neededFor, [Java::int], 1_000_000 # 32

require 'java'


# java_send

# java_alias
class BitLength
java_alias :needed_for_int, :neededFor, [Java::int]
end

bits.needed_for_int 1_000_000 # 32

require 'java'


# java_send

# java_alias
class BitLength
java_alias :needed_for_int, :neededFor, [Java::int]
end

bits.needed_for_int 1_000_000 # 32

# java_method
needed = bits.java_method :neededFor, [Java::int]
needed.call 1_000_000 # 32

... and more about
types

public class TypeChecker{
public static String check(Object o){
return o.getClass().getName();
}
}

require 'java'

ruby_array = [1, 2, 'Mushrooms', :sample]
java_array = ruby_array.to_java

# org.jruby.RubyArray
Java::TypeChecker.check( ruby_array )

# [Ljava.lang.Object;
Java::TypeChecker.check( java_array )

# org.jruby.RubyArray
Java::TypeChecker.check( java_array.to_a )

Sooo, what about those
C extensions... ?

Awesome, but why?
• Cross platform GUI dev
• Performance
• Ruby interface to legacy code
• Use a ruby test framework
(Seriously, they’re amazing!)
• Utilize java libraries
• Sneak ruby into a java shop
• Threading

import org.jruby.embed.InvokeFailedException;
import org.jruby.embed.ScriptingContainer;

public class RubyFromJava {
public static void main(String[] args) {
ScriptingContainer container = new ScriptingContainer();

container.runScriptlet("puts 'Java touched my Ruby'");
}
}

$ java -cp jruby-complete.jar:. RubyFromJava
Java touched my Ruby

http://pragprog.com/book/jruby/using-jruby

http://www.meetup.com/Code-Coffee-JHB/

http://www.meetup.com/RubyOnBeer/

jRuby: The best of both worlds

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Editor's Notes