Модерни езици за програмиране за JVM (2011)

Модерни езици за
програмира за JVM
JRuby, Groovy, Scala и Clojure.

Що е Java?

Програмен език

Виртуална машина

Стандартна библиотека

The beating heart of Java is not the Java
programming language - it is the JVM and the
entire infrastructure built around it...

Maximus Decimus Meridius,
Roman General & Java Programmer

Езикът Java

Създаден да замени С++

Интегрира някои добри идеи от Lisp

Характеризира се с консервативен, но
практичен дизайн

Проблемите на езикът
Java
Не е чист обектно-ориентиран език

Няма никаква поддръжка за функционален
стил на програмиране

Не е особено експресивен

Развитието му е ограничено от
изискванията за обратна съвместимост

Че то алтернативи има
ли?
1996 - Java 1.0

1997 - 40 езика вече имат версия за JVM

2004 - 169 са JVM compatible

2011 - приблизително 300 езика се целят
в JVM

Причината?

The JVM is rock solid and heart touching at
the same time.

Отлична производителност и прекрасен
optimizer

Огромна база съществуващ Java код

Купища страхотни иструменти

Не всичко е ток и жица
Java (< 7) нямаше поддръжка за динамичен
метод dispatching

JVM не е оптимизиран за функционален стил
на програмиране

JVM пали относително бавно

JVM имплементациите на някои езици (като
Python) не са съвсем съвместими с native (C)
имплементациите им

Двете страни на
Силата

Езици портнати към JVM

Езици създадени специално за JVM

Претендентите
JRuby

Jython

Fantom

Groovy

Scala

Clojure

Ruby

динамичен език за програмиране

компактен и елегантен синтаксис

създаден да направи програмистите
щастливи

made in Japan

Сега (като Ruby
програмист)

Hello, Ruby
# Output "I love Ruby"
say = "I love Ruby"
puts say

# Output "I *LOVE* RUBY"
say['love'] = "*love*"
puts say.upcase

# Output "I *love* Ruby"
# five times
5.times { puts say }

JRuby - Java & Ruby
sitting in a tree
Ruby е елегантен език с бавен runtime

JVM е много бърз runtime

JRuby дава възможност на Java
програмистите да използват технологии
като Rails

JRuby дава възможност на Ruby
програмистите да ползват Java
библиотеки

Загрявка в jirb
jruby-1.6.1 :001 > puts "Hello, JRuby"
Hello, JRuby
=> nil
jruby-1.6.1 :002 > arr = ["Chuck", "Sarah", "Morgan", "Casey"]
=> ["Chuck", "Sarah", "Morgan", "Casey"]
jruby-1.6.1 :003 > arr.length
=> 4
jruby-1.6.1 :004 > arr.size
=> 4
jruby-1.6.1 :005 > arr.size()
=> 4
jruby-1.6.1 :006 > arr.each { |name| puts name }
Chuck
Sarah
Morgan
Casey
jruby-1.6.1 :007 > arr.each_with_index { |name, index| puts "##{index}:
#{name}"}
0: Chuck
1: Sarah
2: Morgan
3: Casey

Ако прилича на
патица...
class Duck
def walk
puts "The duck walks"
end

def quack
puts "The duck quacks"
end
end

class Dog
def walk
puts "The dog walks"
end

def quack
puts "The dog quacks"
end
end

def test_animal(animal)
animal.walk
animal.quack
end

test_animal(Duck.new)
test_animal(Dog.new)

Java от Ruby
require 'java'
java_import 'java.lang.System'
java_import 'java.util.ArrayList'
java_import 'javax.swing.JOptionPane'

System.out.println("Feel the power of JRuby")

## using snake_names for Java method names
puts System.current_time_millis
## regular names work as well
puts System.currentTimeMillis

array_list = ArrayList.new

## the array list supports some common Ruby idioms
array_list << 1
array_list.add 2
array_list << 3

puts "List length is ##{array_list.length}"

array_list.each { |elem| puts elem }

## a glimpse of Swing
JOptionPane.show_message_dialog(nil, "This is a message from the future of Ruby!")

Ruby от Java

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 'Ruby bridge
established successfully'" );
}
}

Стана ми интересно,
къде да науча повече?

http://batsov.com/articles/2011/05/18/jvm-
langs-jruby/

It’s a Groovy kind of
love...

Хвала на Groovy
Groovy is like a super version of Java. It can
leverage Java's enterprise capabilities but also has
cool productivity features like closures, builders
and dynamic typing. If you are a developer, tester
or script guru, you have to love Groovy.

def name='World'; println "Hello $name!"

class Greet {
def name
Greet(who) { name = who[0].toUpperCase() +
who[1..-1] }
def salute() { println "Hello $name!" }
}

g = new Greet('world') // create object
g.salute() // output "Hello World!"

import static
org.apache.commons.lang.WordUtils.*

class Greeter extends Greet {
Greeter(who) { name = capitalize(who) }
}

new Greeter('world').salute()

groovy -e "println 'Hello ' + args[0]" World

Groovy e...

динамичен

изцяло обектно-ориентиран

вдъхновен от Ruby, Python и Smalltalk

със синтаксис много близък до този на
Java

създаден да улесни живота на Java
програмистите

Ключовите моменти

closures

attributes

duck typing

аритметика базирана на BigDecimal

улеснена работа с XML, SQL, Swing, etc

Groovy & Java
Groovy програмите се компилират до Java
bytecode

Същите низове, същите регулярни изрази и т.н.

Същите API

Същия модел за сигурност, същия нишков
модел

Същите ОО концепции

// old school Java code, but also valid Groovy code
System.out.println("Hello, world!");

// idiomatic Groovy
println "Hello, world!"

// dynamic variable definition
def name = "Bozhidar"

// GString featuring string interpolation
println "Hello, $name" // => "Hello, Bozhidar"

// statically typed variable
String songName = "Coding in the Name of"

println "Now playing - $songName"

String multiline = """this is a multiline
string. There is not need to embed
newline characters in it"""

println multiline

// method definition
def greet(name) {
println "Hello, $name!"
}

// method invocation
greet "Bozhidar"
greet("Bozhidar")

showSize([1, 2, 3])
// this is the important part
showSize(null)

// a list
def beers = ["Zagorka", "Bolyarka", "Shumensko", "Ariana"]

// list access
println "My favourite beer is ${beers[1]}"

beers.each { beer -> println beer }

// imports can appear anywhere and support the creation of
aliases
import static java.util.Calendar.getInstance as now
import java.sql.Date as SDate

println now()
// java.util package is automatically imported in Groovy so this
is java.util.Date
println new Date()
println new SDate(2011, 5, 5)

// language support for regular expressions
if ("Hello, Groovy" =~ /w+,sw+/) {
println "It matches"
}

// range filtering with higher-order functions
(1..10).findAll { n -> n % 2 == 0}.each { n -> println n }

// map
def capitols = [Bulgaria: "Sofia", USA: "Washington", England:"London", France:"Paris"]

println capitols["Bulgaria"] // => Sofia
println capitols["France"] // => Paris

// class definition
class Person {
def name
def age

Person(name, age) {
this.name = name
this.age = age
}

@Override
String toString() {
return "Name {$name}, age {$age}"
}
}

def me = new Person("Bozhidar", 26)
println me

JDBC подобрения
import groovy.sql.Sql
sql = Sql.newInstance("jdbc:mysql://host/db", "username", "password",
"com.mysql.jdbc.Driver")
sql.eachRow("select * from tableName", { println it.id + " -- ${it.firstName} --"} )

Изход от програмата
1 -- Bozhidar --
2 -- Jim --
3 -- Jack --
4 -- Valentine --

XML
<books>
<book>
<title>Dune</title>
<author firstname="Frank" lastname="Herbert"/>
</book>
<book>
<title>Dune Messiah</title>
</book>
<book>
<title>Children of Dune</title>
</book>
<book>
<title>A Game of Thrones</title>
<author firstname="George" lastname="Martin"/>
</book>
</books>

def books = new XmlSlurper().parse("books.xml")
books.book.each {
println "Title = ${it.title}, Author: ${it.author.@firstname} ${it.author.@lastname}"
}

Builders
import groovy.xml.* <html>
<head>
def page = new MarkupBuilder() <title>Hello, Groovy!</
page.html { title>
head { title 'Hello, Groovy!' } </head>
body { <body>
div { <div>
3.times { <p>Groovy power!</p>
p "Groovy power!" <p>Groovy power!</p>
} <p>Groovy power!</p>
} </div>
} </body>
} </html>

Swing
import java.awt.FlowLayout

builder = new groovy.swing.SwingBuilder()
langs = ["Groovy", "Scala", "Clojure"]
gui = builder.frame(size: [290, 100], title: 'Groovy Swing') {
panel(layout: new FlowLayout()) {
panel(layout: new FlowLayout()) {
for (lang in langs) {
radioButton(text: lang)
}
}
button(text: 'Perform Magic', actionPerformed: {
builder.optionPane(message: "Feel the power of Groovy!").
createDialog(null, 'Message').show()
})
button(text: 'Quit',
actionPerformed: {System.exit(0)})
}
}
gui.show()

Инструментите на
занаята

groovy - интерпретатор

groovysh - конзола

groovyc - компилатор

groovyconsole - графична конзола

Приложения убийци
(killer apps)
Grails - модерна платформа за разработка
на уеб приложения, вдъхновена от Ruby on
Rails

Gradle - могъщ build tool, създаден да
наследи Maven

Griffon - модерна платформа за
разработка на Swing приложения

IDE-та, нещо?

IntelliJ IDEA - Bozhidar’s Choice

Eclipse

NetBeans

Where do we go now?

langs-groovy/

Ride the eSCALAtor

If I were to pick a
language to use today
other than Java, it would
be Scala...

James Gosling, father of Java

Отмъщението на статично
типизираните езици
Scala е статично типизиран език (като
Java)

Scala използва type inference механизъм,
който сериозно намалява типовите
декларации

Кодът написан на Scala е толкова сигурен
и бърз, колкото този написан на Java

ООП и ФП могат да
съжителстват в мир и любов
Scala е чисто обектно-ориентиран език

Scala включва в себе си много елементи от
функционалното програмиране

higher order functions

function objects

pattern matching

tail recursion

Expressive

scala> val romanToArabic = Map("I" -> 1, "II" -> 2, "III" -> 3, "IV" -> 4, "V" -> 5)
romanToArabic: scala.collection.immutable.Map[java.lang.String,Int] = Map((II,2),
(IV,4), (I,1), (V,5), (III,3))

scala> romanToArabic("I")
res2: Int = 1

scala> romanToArabic("II")
res3: Int = 2

Компактен код, без
излишна церемония
public boolean hasUpperCase(String word) {
if (word == null) {
return false;

Java }
int len = word.length();
for (int i = 0; i < len; i++) {
if (Character.isUpperCase(word.charAt(i))) {
return true;
}
}
return false;
}

Scala
def hasUppercase(word: String) = if (word != null) word.exists(_.isUpperCase) else false

Оптимизиран за
Java мързели
class Person {
private String name;
private int age;

Person(String name, int age) {
this.name = name;
this.age = age;
}

public String getName() {
Scala
return name;
} class Person(var name: String, var age: Int)

public void setName(String name) {
this.name = name;
}

public int getAge() {
return age;
}

public void setAge(int age) {
this.age = age;
}
}

Актьорско майсторство
import scala.actors.Actor._

case class Add(x: Int, y: Int)
case class Sub(x: Int, y: Int)

val mathService = actor {
loop {
receive {
case Add(x, y) => reply(x + y)
case Sub(x, y) => reply(x - y)
}
}
}

mathService !? Add(1, 3) // returns 4
mathService !? Sub(5, 2) // returns 3

Патоците на власт!
class Duck {
def quack = println("The duck quacks")
def walk = println("The duck walks")
}

class Dog {
def quack = println("The dog quacks (barks)")
def walk = println("The dog walks")
}

def testDuckTyping(animal: { def quack; def walk }) = {
animal.quack
animal.walk
}

scala> testDuckTyping(new Duck)
The duck quacks
The duck walks

scala> testDuckTyping(new Dog)
The dog quacks (barks)
The dog walks

Pimp my library
scala> implicit def intarray2sum(x: Array[Int]) = x.reduceLeft(_ + _)
intarray2sum: (x: Array[Int])Int

scala> val x = Array(1, 2, 3)
x: Array[Int] = Array(1, 2, 3)

scala> val y = Array(4, 5, 6)
y: Array[Int] = Array(4, 5, 6)

scala> val z = x + y
z: Int = 21

Малко повече екшън
scala> println("Hello, Scala")
Hello, Scala

scala> val name = "Bozhidar"
name: java.lang.String = Bozhidar

scala> Predef.println("My name is "+name)
My name is Bozhidar

scala> var someNumber: Int = 5
someNumber: Int = 5

scala> var names = Array("Superman", "Batman", "The Flash", "Bozhidar")
names: Array[java.lang.String] = Array(Superman, Batman, The Flash,
Bozhidar)

scala> names.filter(name => name.startsWith("B"))
res6: Array[java.lang.String] = Array(Batman, Bozhidar)

scala> names.length
res7: Int = 4

scala> name.length()
res8: Int = 8

...
scala> import java.util.Date
import java.util.Date

scala> var currentDate = new Date
currentDate: java.util.Date = Wed May 11 15:03:20 EEST 2011

scala> println("Now is " + currentDate)
Now is Wed May 11 15:03:20 EEST 2011

scala> currentDate.toString
res10: java.lang.String = Wed May 11 15:03:20 EEST 2011

scala> currentDate.toString()

scala> currentDate toString

Closures
scala> var x = 10
x: Int = 10

scala> val addToX = (y: Int) => x + y
addToX: (Int) => Int = <function1>

scala> addToX(2)
res0: Int = 12

scala> addToX(6)
res1: Int = 16

scala> x = 5
x: Int = 5

scala> addToX(10)
res2: Int = 15

Свързани списъци
scala> 1 :: 2 :: 3 :: 4 :: 5 :: Nil
res3: List[Int] = List(1, 2, 3, 4, 5)

scala> val names = List("Neo", "Trinity", "Morpheus", "Tank", "Dozer")
names: List[java.lang.String] = List(Neo, Trinity, Morpheus, Tank,
Dozer)

scala> names.length
res4: Int = 5

scala> names.foreach(println)
Neo
Trinity
Morpheus
Tank
Dozer

scala> names.map(_.toUpperCase)
res6: List[java.lang.String] = List(NEO, TRINITY, MORPHEUS, TANK,
DOZER)

scala> names.forall(_.length > 5)
res7: Boolean = false

scala> names.forall(_.length > 2)
res8: Boolean = true

...
scala> names.filter(_.startsWith("T"))
res9: List[java.lang.String] = List(Trinity, Tank)

scala> names.exists(_.length == 3)
res10: Boolean = true

scala> names.drop(2)
res11: List[java.lang.String] = List(Morpheus, Tank, Dozer)

scala> names.reverse
res12: List[java.lang.String] = List(Dozer, Tank, Morpheus, Trinity, Neo)

scala> names.sortBy(_.length)
res13: List[java.lang.String] = List(Neo, Tank, Dozer, Trinity, Morpheus)

scala> names.sort(_ > _)
res14: List[java.lang.String] = List(Trinity, Tank, Neo, Morpheus, Dozer)

scala> names.slice(2, 4)
res16: List[java.lang.String] = List(Morpheus, Tank)

Pattern matching
scala> def testMatching(something: Any) = something match {
| case 1 => "one"
| case "two" => 2
| case x: Int => "an integer number"
| case x: String => "some string"
| case <xmltag>{content}</xmltag> => content
| case head :: tail => head
| case _ => "something else entirely"
| }
testMatching: (something: Any)Any

scala> testMatching(1)
res18: Any = one

scala> testMatching("two")
res19: Any = 2

scala> testMatching(2)
res20: Any = an integer number

scala> testMatching("matrix")
res21: Any = some string

scala> testMatching(<xmltag>this is in the tag</xmltag>)
res22: Any = this is in the tag

scala> testMatching(List(1, 2, 3))
res23: Any = 1

scala> testMatching(3.9)
res24: Any = something else entirely

Plain recursion

def length(list: List[Any]): Int = list match {
case head :: tail => 1 + length(tail)
case Nil => 0
}

Tail recursion
def length(list: List[Any]): Int = {
def lengthrec(list: List[Any], result: Int): Int =
list match {
case head :: tail => lengthrec(tail, result + 1)
case Nil => result
}

lengthrec(list, 0)
}

Инвентара

scala - конзола/интерпретатор

scalac - компилатор

fsc - fast scala compiler

IDE-тата

IntelliJ IDEA - Bozhidar’s Choice

Eclipse - Ofﬁcial Scala IDE

NetBeans - на тоя етап е бран бостан

Убийците

Play! Framework

Lift

SBT (Simple Build Tool)

Akka

The full disclosure on
Clojure

“Clojure feels like a general-purpose language
beamed back from the near future. Its support
for functional programming and software trans-
actional memory is well beyond current practice
and is well suited for multicore hardware. At the
same time, Clojure is well grounded in the past
and the present. It brings together Lisp and the
Java Virtual Machine. Lisp brings wisdom spanning
most of the history of programming, and Java
brings the robustness, extensive libraries, and
tooling of the dominant platform available today.”

What happens when an
unstoppable force meets an
immutable object?

Clojure is dynamic

Clojure is functional

Clojure is a Lisp(1)

Clojure is designed for concurrency

Clojure is ﬁghting accidental complexity

Стил
public boolean hasUpperCase(String word) {
if (word == null) {
return false;
}
int len = word.length();
for (int i = 0; i < len; i++) {
if (Character.isUpperCase(word.charAt(i))) {
return true;
}
}
return false;
}

(defn has-uppercase? [string]
(some #(Character/isUpperCase %) string))

Компактност
class Person {
private String name;
private int age;

Person(String name, int age) {
this.name = name;
this.age = age;
}

public String getName() {
return name; (defrecord person [name age])
}

public void setName(String name) {
this.name = name;
}

public int getAge() {
return age;
}

public void setAge(int age) {
this.age = age;
}
}

Силата е на ваша
страна
(defmacro and
"Evaluates exprs one at a time, from left to
right. If a form
returns logical false (nil or false), and returns
that value and
doesn't evaluate any of the other expressions,
otherwise it returns
the value of the last expr. (and) returns true."
{:added "1.0"}
([] true)
([x] x)
([x & next]
`(let [and# ~x]
(if and# (and ~@next) and#))))

;;; Lists
;; list creation
user> (list 1 2 3)
(1 2 3)
Сърцето на Clojure
;; quoted list creation
user> (def a-list '(1 2 3 4 5 6 7 8 9 10))
#'user/a-list
;; find the size of a list
user> (count a-list)
10
user> (first a-list)
1
user> (rest a-list)
(2 3 4 5 6 7 8 9 10)
user> (last a-list)
10
;; find the elements of the list matching a predicate(boolean
function)
user> (filter even? a-list)
(2 4 6 8 10)
user> (filter odd? a-list)
(1 3 5 7 9)
;; map an anonymous(lambda) function to all elements of the list
user> (map #(* % 2) a-list)
(2 4 6 8 10 12 14 16 18 20)
;; add an element to the beginning of the list
user> (cons 0 a-list)
(0 1 2 3 4 5 6 7 8 9 10)
;; cons in a list specific function, conj is a general purpose one and
;; works on all collection (but in a different manner)
user> (conj a-list 0)
(0 1 2 3 4 5 6 7 8 9 10)

;; retrieve the first five items in a list
user> (take 5 a-list)
...
(1 2 3 4 5)
;; retrieve all but the first five items in a list
user> (drop 5 a-list)
(6 7 8 9 10)
user> (take-while #(< % 3) a-list)
(1 2)
user> (drop-while #(> % 3) a-list)
(1 2 3 4 5 6 7 8 9 10)
user> (drop-while #(< % 3) a-list)
(3 4 5 6 7 8 9 10)

;;; Sets

user> (set '(1 2 3 4 5 1 2 3 4))
#{1 2 3 4 5}
user> (def a-set #{1 2 3 4 5})
#'user/a-set
user> (contains? a-set 3)
true
user> (contains? a-set 7)
false
user> (conj a-set 5)
#{1 2 3 4 5}
user> (conj a-set 6)
#{1 2 3 4 5 6}
user> (disj a-set 1)
#{2 3 4 5}
user> (get a-set 1)
1
user> (get a-set 7)
nil

Хешове

;;; Maps
user> (hash-map :Bozhidar :Batsov :Bruce :Wayne :Selina :Kyle)
{:Selina :Kyle, :Bozhidar :Batsov, :Bruce :Wayne}
user> (def a-map {:Bozhidar :Batsov, :Bruce :Wayne, :Selina :Kyle})
#'user/a-map
user> a-map
{:Bozhidar :Batsov, :Bruce :Wayne, :Selina :Kyle}
user> (get a-map :Bozhidar)
:Batsov
user> (contains? a-map :Bozhidar)
true
user> (contains? a-map :Clark)
false
user> (:Bozhidar a-map)
:Batsov
user> (assoc a-map :Lois :Lane)
{:Lois :Lane, :Bozhidar :Batsov, :Bruce :Wayne, :Selina :Kyle}
user> (keys a-map)
(:Bozhidar :Bruce :Selina)
user> (vals a-map)
(:Batsov :Wayne :Kyle)
user> (dissoc a-map :Bruce)
{:Bozhidar :Batsov, :Selina :Kyle}
user> (merge a-map {:Alia :Atreides, :Arya :Stark})
{:Arya :Stark, :Alia :Atreides, :Bozhidar :Batsov, :Bruce :Wayne, :Selina :Kyle}

Вектори
;;; Vectors

user> (vector 1 2 3 4)
[1 2 3 4]
user> [1 2 3 4]
[1 2 3 4]
user> (def a-vector [1 2 3 4 5])
#'user/a-vector
user> (count a-vector)
5
user> (conj a-vector 13)
[1 2 3 4 5 13]
;; random access is a constant time operation in
vectors
user> (nth a-vector 3)
4
user> (pop a-vector)
[1 2 3 4]
user> (peek a-vector)
5

Програмиране с refs
(def picked-numbers (ref #{})

(def secret-num (.nextInt (java.util.Random.) 10))

(defn guess-number [n]
(print "Enter a guess between 1 and 10: ")
(flush)
(let [guess (java.lang.Integer/parseInt (read-line)) ]
(cond
(= guess n) (println "You guessed correctly")
(contains? (deref picked-numbers) n) (println "Pick another number!
You already tried that one.")
:else (dosync
(alter picked-numbers conj guess)))))

user=> (guess-number secret-num)
Enter a guess between 1 and 10: 1
#{1}
#{1 3}
#{1 3 5}

Атоми

(def picked-numbers (atom #{})

(def secret-num (.nextInt (java.util.Random.) 10))

(defn guess-number [n]
(print "Enter a guess between 1 and 10: ")
(flush)
(let [guess (java.lang.Integer/parseInt (read-line)) ]
(cond
(= guess n) (println "You guessed correctly")
(contains? (deref picked-numbers) n) (println "Pick another number!
You already tried that one.")
:else (swap! picked-numbers conj guess))))

#{1}
#{1 3}
#{1 3 5}

ООП по
Лиспаджийски

(defmulti my-add (fn [x y] (and (string? x) (string? y))))

(defmethod my-add true [x y]
(str x y))

(defmethod my-add false [x y]
(+ x y))

user=> (my-add 3 4) ; => 7
user=> (my-add "3" "4") ; => "34"

Екстремист съм, какво
ми трябва?
Обичайните заподозрени

Eclipse

IntelliJ

NetBeans

Emacs + SLIME = Bozhidar’s Choice

Повече инфо, моля!

langs-clojure/

Модерни езици за програмиране за JVM (2011)

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