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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 [email protected] (company)www.SphericalImprovement.com (blog)
Interested in learning more about how Ruby and Java can coexist in your company? Just ask me.