Ruby for Java ProgrammersRuby for Java Programmers

Mike BowlerPresident, Gargoyle Software Inc.

Mike BowlerPresident, Gargoyle Software Inc.

Why learn another language?

Why Ruby?

Timeline: 1993 to 2000Timeline: 1993 to 2000

Created in 1993 by Yukihiro "Matz" Matsumoto

Ruby was popular in Japan but unknown everywhere else

All documentation was written in Japanese

Timeline: 2000-2004Timeline: 2000-2004

First English language book published in 2000

A lot of interest in the Agile development community but mostly unknown elsewhere

Timeline: 2004-todayTimeline: 2004-today

The Ruby on Rails framework has pushed ruby into the spotlight

This is the “killer app”

What influenced it?What influenced it?

TerminologyTerminology

Early

Late

Static

Dynamic

Strong

Weak

Defining strong/weak typing

Defining strong/weak typing

Strong typing

Objects are of a specific type and will not be converted automatically

Java: “4”/2 results in a compile error

Weak typing

Objects can be converted under the covers at any time

Perl: ‘4’/2 => 2

Ruby is strongly typed

Early/late bindingEarly/late bindingEarly binding (aka static binding)

All method invocations must be defined at compile time

Java: foo.getUser()

Late binding (aka dynamic binding)

The runtime does not check that a given method exists until an attempt to invoke it

Smalltalk: foo user.

Ruby uses late binding

SimilaritiesSimilarities

Like Java, Ruby...

runs on a virtual machine

is garbage collected

is object oriented (although to different degrees)

DifferencesDifferences

Everything is an object

Javastring = String.valueOf(1);

Rubystring = 1.to_s()

Primitive

Object

DifferencesDifferences

Many things that you would expect to be keywords are actually methods

throw new IllegalArgumentException("oops");

raise TypeError.new("oops")

Keywords

Methods

DifferencesDifferencesSome syntax optional unless the result is ambiguous

These statements are equivalent

puts("foo");

puts "foo"Idiomatic (better) style

DifferencesDifferencesClasses are real objects

They’re instances of Class

Class methods can be overridden

class ZebraCage < Cage attr_accessor :capacity @@allCages = Array.new

def initialize maximumZebraCount @capacity = maximumZebraCount @@allCages << self end

private def clean_cage # do some stuff here endend

cage = ZebraCage.new 10puts cage.capacity

Multiline ifMultiline ifif name.nil? do_somethingend

Multiline ifMultiline ifif name.nil? do_somethingend

Notice thequestion mark

With an elseWith an elseif name.nil? do_somethingelse something_elseend

Single line ifSingle line ifif name.nil? do_somethingend

do_something if name.nil?

Both kinds of unlessBoth kinds of unlessif name.nil? do_somethingend

do_something if name.nil?

unless name.nil? do_somethingend

do_something unless name.nil?

Dangerous methodsDangerous methods

name = " foo "

name.strip

name.strip!

Returns a new string.Doesn’t modify name.

Modifies name and returns that.

Dangerous!

PhilosophyPhilosophyJava focuses on building blocks

You can build whatever you want with the pieces

Ruby focuses on solving problems

Things you do frequently should be concise

Initializing arraysInitializing arraysList<String> list = new ArrayList<String>();list.add("foo");list.add("bar");

Same only rubySame only rubyList<String> list = new ArrayList<String>();list.add("foo");list.add("bar");

list = Array.newlist << 'foo'list << 'bar'

[][]List<String> list = new ArrayList<String>();list.add("foo");list.add("bar");

list = Array.newlist << 'foo'list << 'bar'

list = ['foo', 'bar']

%w()%w()List<String> list = new ArrayList<String>();list.add("foo");list.add("bar");

list = Array.newlist << 'foo'list << 'bar'

list = ['foo', 'bar']

list = %w(foo bar)

In fairness to java...In fairness to java...List<String> list = new ArrayList<String>();list.add("foo");list.add("bar");

List<String> list = Arrays.asList("foo", "bar");

list = Array.newlist << 'foo'list << 'bar'

list = ['foo', 'bar']

list = %w(foo bar)

Same idea with hashes

Same idea with hashes

Map<String,String> map = new HashMap<String,String>();map.put("foo", "one");map.put("bar", "two");

map = {'foo' => 'one', 'bar' => 'two'}

Special case for Hash

Special case for Hash

hash = {:a => 5, :b => 3}do_stuff 30, hash

do_stuff 100, :a => 5, :b => 3

Regular ExpressionsRegular Expressions

Pattern pattern = Pattern.compile("^\\s*(.+)\\s*$");Matcher matcher = pattern.matcher(line);if( matcher.matches() ) { doSomething();}

Regular ExpressionsRegular Expressions

Pattern pattern = Pattern.compile("^\\s*(.+)\\s*$");Matcher matcher = pattern.matcher(line);if( matcher.matches() ) { doSomething();}

do_something if line =~ /^\s*(.+)\s*$/

Nil and NullNil and NullJava’s nullJava’s null Ruby’s nilRuby’s nil

Absence of an object An instance of NilClass

if( a != null ) {...} unless a.nil? {...}

null.toString() -> NPE nil.to_s -> “”

null.getUser() ->Exception in thread "main" java.lang.NullPointerException

nil.get_user -> NoMethodError: undefined method ‘get_user’ for nil:NilClass

Implications of late binding

Implications of late binding

Method dispatch is quite different

Ruby makes a distinction between “messages” that are sent to an object and the “methods” that get dispatched

Message != MethodMessage != Method

What if there isn’t a method for the specified

message?

What if there isn’t a method for the specified

message?

method_missing example from ActiveRecord

method_missing example from ActiveRecord

user = Users.find_by_name(name)

user = Users.find(:first, :conditions => [ "name = ?", name])

Creating proxy objects

Creating proxy objects

Mock object for testing

Proxy object to allow distributed objects across machines

Wrapper to record usage of a given object

Implementing a proxyImplementing a proxyclass Proxy def method_missing name, *args, &proc puts name,args endend

Implementing a proxyImplementing a proxyclass Proxy def method_missing name, *args, &proc puts name,args endend

Proxy.new.foo_bar ‘a’Proxy.new.to_s

Dispatches to method_missing

Doesn’t go to method_missing

Overriding to_sOverriding to_sclass Proxy def method_missing name, *args, &proc puts name,args end

def to_s method_missing :to_s, [] endend

=•===•=~•__id__•_send__•class•clone•dclonedisplay•dup•enum_for•eql?•equal?•extend freeze

frozen?•hash•id•inspect•instance_eval instance_of?

instance_variable_defined•instance_variable_getinstance_variable_get•instance_variable_set

instance_variable_set•instance_variables•is_a?kind_of?•method•methods•new•nil?•object_id

private_methods•protected_methods•public_meth

odsremove_instance_variable•respond_to?•send

singleton_method_added•singleton_method_removed

singleton_method_undefined•singleton_methods•taint

tainted?•to_a•to_enum•to_s•to_yamlto_yaml_properties•to_yaml_style•type•untaint

Implementing a proxyImplementing a proxy

class Proxy instance_methods.each do |method| undef_method method unless method =~ /^__/ end

def method_missing name, *args, &proc puts name,args endend

Proxy.new.to_s

Unix was not designed to stop people from doing stupid things, because that would also stop them from doing clever things.

—Doug Gwyn

Cultural differences about type

Cultural differences about type

Java is very focused on the types of objects

Is the object an instance of a specific class?

Or does it implement a specific interface?

Ruby is focused on the behaviour

Does the object respond to a given message?

TypesTypes

public void foo( ArrayList list ) { list.add("foo");}

def foo list list << 'foo'end

What’s the type?

What’s the type?

Duck typingDuck typingdef foo list list << 'foo'end

If list is a String=> ‘foo’

If list is an Array=> [‘foo’]

If list is an IO=> string will be written to stream

Duck typingDuck typing

Duck typing implies that an object is interchangeable with any other object that implements the same interface, regardless of whether the objects have a related inheritance hierarchy. -- Wikipedia

"If it walks like a duck and quacks like a duck, it must be a duck." -- Pragmatic Dave Thomas

How does this change how wethink of types?

How does this change how wethink of types?

Overflow conditionsOverflow conditions

int a = Integer.MAX_VALUE;System.out.println(" a="+a);System.out.println("a+1="+(a+1));

a=2147483647a+1= ??

Overflow conditionsOverflow conditions

int a = Integer.MAX_VALUE;System.out.println(" a="+a);System.out.println("a+1="+(a+1));

a=2147483647a+1=-2147483648

oops

Overflow in ruby?Overflow in ruby?

number = 10001.upto(4) do puts "#{number.class} #{number}" number = number * numberend

Fixnum 1000Fixnum 1000000Bignum 1000000000000Bignum 1000000000000000000000000

ClosuresClosures

A closure is a function that is evaluated in an environment containing one or more bound variables. When called, the function can access these variables. The explicit use of closures is associated with functional programming and with languages such as ML and Lisp. Constructs such as objects in other languages can also be modeled with closures. -- Wikipedia

ClosuresClosures

A closure is a block of code that you can manipulate and query

In Ruby we call them blocks or Procs

A block is a pure closure

A Proc is a block wrapped as an object

We generally use the terms block and Proc interchangeably

ClosuresClosures

multiplier = 5block = lambda {|number| puts number * multiplier }

A block

An instanceof Proc

lambda() is a method to convertblocks into Procs

ClosuresClosures

multiplier = 5block = lambda {|number| puts number * multiplier }

Parameterto the block

ClosuresClosures

multiplier = 5block = lambda {|number| puts number * multiplier }

Able to access variables from outside the block

Proc’sProc’s

multiplier = 5block = lambda {|number| puts number * multiplier }block.call 2

block.arityprints 10

returns number of parametersthat the block takes. 1 in this case

Blocks as parametersBlocks as

parametersmultiplier = 51.upto(3) {|number| puts number * multiplier }

=> 5=> 10=> 15

Same blockas before

Called once for each timethrough the loop

Alternate syntaxAlternate syntax

multiplier = 51.upto(3) {|number| puts number * multiplier }

1.upto(3) do |number| puts number * multiplierend

Equivalent

Why are closures significant?

Why are closures significant?

Presence of closures in a language completely changes the design of the libraries

Closure based libraries generally result in significantly less code

// Read the lines and split them into columnsList<String[]> lines= new ArrayList<String[]>();BufferedReader reader = null;try { reader = new BufferedReader(new FileReader("people.txt")); String line = reader.readLine(); while( line != null ) { lines.add( line.split("\t") ); }}finally { if( reader != null ) { reader.close(); }}

// then sortCollections.sort(lines, new Comparator<String[]>() { public int compare(String[] one, String[] two) { return one[1].compareTo(two[1]); }});

// then write them back outBufferedWriter writer = null;try { writer = new BufferedWriter( new FileWriter("people.txt") ); for( String[] strings : lines ) { StringBuilder builder = new StringBuilder(); for( int i=0; i<strings.length; i++ ) { if( i != 0 ) { builder.append("\t"); } builder.append(strings[i]); } }}finally { if( writer != null ) { writer.close(); }}

# Load the datalines = Array.newIO.foreach('people.txt') do |line| lines << line.splitend

# Sort and write it back outFile.open('people.txt', 'w') do |file| lines.sort {|a,b| a[1] <=> b[1]}.each do |array| puts array.join("\t") endend

Closure File ExampleClosure File Examplefile = File.new(fileName,'w')begin file.puts ‘some content’rescue file.closeend

Closure File ExampleClosure File Examplefile = File.new(fileName,'w')begin file.puts ‘some content’rescue file.closeend Only one line of

business logic

Closure File ExampleClosure File Examplefile = File.new(fileName,'w')begin file.puts ‘some content’rescue file.closeend

File.open(fileName,'w') do |file| file.puts ‘some content’end

Ruby file IO sampleRuby file IO sample

# Load the datalines = Array.newIO.foreach('people.txt') do |line| lines << line.splitend

# Sort and write it back outFile.open('people.txt', 'w') do |file| lines.sort {|a,b| a[1] <=> b[1]}.each do |array| puts array.join("\t") endend

Closure-like things in Java

Closure-like things in Java

final String name = getName();new Thread( new Runnable() { public void run() { doSomething(name); }}).start();

Only one line ofbusiness logic

Closures for Java?Closures for Java?There are a couple of proposals being debated for Java7

Unclear whether any of them will be accepted

In the past, Sun’s position has been that closures didn’t make sense at this point in Java’s evolution

public static void main(String[] args) { int plus2(int x) { return x+2; } int(int) plus2b = plus2; System.out.println(plus2b(2)); }

Inheriting behaviour from multiple placesInheriting behaviour from multiple places

C++ has multiple inheritance

Java has interfaces

Ruby has mixins

C++ : multiple inheritance

C++ : multiple inheritance

Java : inheritanceJava : inheritance

Ruby : mixinsRuby : mixins

MixinsMixins

Cannot be instantiatedCan be mixed in

EnumerableEnumerable

class Foo include Enumerable

def each &block block.call 1 block.call 2 block.call 3 endend

module Enumerable def collect array = [] each do |a| array << yield(a) end array endend

EnumerableEnumerable

class Foo include Enumerable

def each &block block.call 1 block.call 2 block.call 3 endend

module Enumerable def collect array = [] each do |a| array << yield(a) end array endend

EnumerableEnumerableRequires that the class implement each()

For max, min and sort the <=> operator is also needed

Adds many methods for modifying, searching, sorting the items

all?, any?, collect, detect, each_cons, each_slice, each_with_index, entries, enum_cons, enum_slice, enum_with_index, find, find_all, grep, include?, inject, map, max, member?, min, partition, reject, select, sort, sort_by, to_a, to_set, zip

Reopening classesReopening classesclass Foo def one puts 'one' endend

Reopening classesReopening classesclass Foo def one puts 'one' endend

class Foo def two puts 'two' endend

Reopening the same class

Reopening classesReopening classesclass Foo def one puts 'one' endend

class Foo def one puts '1' endend

Replacing, notadding a method

Reopening core classesReopening core classesclass String def one puts 'one' endend

We reopened a CORE class

and modified it

MetaprogrammingMetaprogramming

Metaprogramming is the writing of computer programs that write or manipulate other programs (or themselves) as their data. In many cases, this allows programmers to get more done in the same amount of time as they would take to write all the code manually.

-- Wikipedia

What changes can we make at

runtime?

What changes can we make at

runtime?

Anything we can hand code, we can programmatically do

Because of late binding, EVERYTHING happens at runtime

attr_accessorattr_accessor

class Foo attr_accessor :barend

class Foo def bar @bar end def bar=(newBar) @bar = newBar endend

Getter

Setter

class Foo def self.attr_accessor name module_eval <<-DONE def #{name}() @#{name} end def #{name}=(newValue) @#{name} = newValue end DONE end my_attr_accessor :barend

Possible implementation of attr_accessor

Possible implementation of attr_accessor

class Foo def self.attr_accessor name module_eval <<-DONE def #{name}() @#{name} end def #{name}=(newValue) @#{name} = newValue end DONE end my_attr_accessor :barend

Possible implementation of attr_accessor

Possible implementation of attr_accessor

“Here Doc”Evaluates to

String

class Foo def self.attr_accessor name module_eval <<-DONE def #{name}() @#{name} end def #{name}=(newValue) @#{name} = newValue end DONE end my_attr_accessor :barend

Possible implementation of attr_accessor

Possible implementation of attr_accessor

Stringsubstitution

class Foo def self.attr_accessor name module_eval <<-DONE def #{name}() @#{name} end def #{name}=(newValue) @#{name} = newValue end DONE end my_attr_accessor :barend

Possible implementation of attr_accessor

Possible implementation of attr_accessor

Executes the stringin the context of

the class

ResultResult

class Foo def bar @bar end def bar=(newBar) @bar = newBar endend

ActiveRecordActiveRecord

class ListItem < ActiveRecord::Base belongs_to :amazon_item acts_as_taggable acts_as_list :scope => :userend

Date :: onceDate :: once

def once(*ids) # :nodoc: for id in ids module_eval <<-"end;", __FILE__, __LINE__ alias_method :__#{id.to_i}__, :#{id.to_s} private :__#{id.to_i}__ def #{id.to_s}(*args, &block) if defined? @__#{id.to_i}__ @__#{id.to_i}__ elsif ! self.frozen? @__#{id.to_i}__ ||= __#{id.to_i}__(*args, &block) else __#{id.to_i}__(*args, &block) end end end; endend

ObjectSpaceObjectSpaceObjectSpace.each_object do |o| puts o end

ObjectSpace.each_object(String) do |o| puts o end

ObjectSpaceObjectSpaceObjectSpace.each_object do |o| puts o end

ObjectSpace.each_object(String) do |o| puts o end

All objects

Only Strings

ContinuationsContinuations

A snapshot of the call stack that the application can revert to at some point in the future

Why continuations?Why continuations?

To save the state of the application across reboots of the VM

To save the state of the application across requests to a web server

Seaside (smalltalk) does this today

DownsidesDownsidesOnly supported in one implementation of Ruby

Will be removed from the language in Ruby 2.0

ImplementationsImplementationsRuby 1.8.x - “reference implementation” in C

Ruby 1.9 - Next version of C interpreter

Rubinius - Ruby in Ruby (sort-of)

Cardinal - Ruby on Parrot

Iron Ruby - Ruby on the DLR (Microsoft)

Ruby.NET - Ruby on the CLR

JRuby - Ruby on the JVM (Sun)

ImplementationsImplementationsRuby 1.8.x - “reference implementation” in C

Ruby 1.9 - Next version of C interpreter

Rubinius - Ruby in Ruby (sort-of)

Cardinal - Ruby on Parrot

Iron Ruby - Ruby on the DLR (Microsoft)

Ruby.NET - Ruby on the CLR

JRuby - Ruby on the JVM (Sun)

JRubyJRubyRuns on the Java Virtual Machine (JVM)

Full implementation of the Ruby language

Supported by Sun

Runs many benchmarks faster than the 1.8 reference implementation (written in C)

Able to easily call out to Java code

Ruby on RailsRuby on Rails

Web application framework

Sweet spot - web application talking to a single relational database

Allows very rapid development of web apps

Who’s using rails?Who’s using rails?

Amazon • BBC • Cap Gemini Chicago Tribune • Barclays • BPN • Cisco

CNET Electronic Arts • IBM • John Deere JP Morgan Chase • LA Times • Limewire Linked In • NASA • NBC • New York Times

Oakley • Oracle • Orbitz • Turner Media twitter.com • Siemens • ThoughtWorks

Yahoo!

JRuby on Rails?JRuby on Rails?Yes! You can run a rails application on JRuby in a servlet container

Goldspike is the servlet that dispatches to rails

Tested on WebLogic, WebSphere, GlassFish, Jetty, Tomcat

Warbler is the packaging tool that makes the WAR

Supported on: WebLogic, WebSphere, GlassFish, Jetty, Tomcat

RecapRecap

Learning a new language will make you better with all the languages you know

Ruby has a much more concise syntax which means that it takes much less code to solve the same problems

Ruby is able to run on the JVM which makes it an option for shops with heavy investments in J2EE infrastructure

RecapRecapEverything is an object

The language is extremely malleable

New classes/methods can be created on the fly

Existing classes can be modified at any time

Contacting meContacting me

Mike Bowlermbowler@GargoyleSoftware.comwww.GargoyleSoftware.com (company)www.SphericalImprovement.com (blog)

Interested in learning more about how Ruby and Java can coexist in your company? Just ask me.