A Tour of Groovy

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A Tour of Groovy

• Chris Wong
• cwong_at_makanasolutions.com

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Your code in Java

• enum PeriodType WEEKLY, MONTHLY, QUARTERLY,
  ANNUALLY
• _at_Entity
• class Invoice
• _at_Id
• int id
• _at_OneToMany
• ListltItemgt items
• PeriodType periodType
• public ListltItemgt getFunnyItems()
• ListltItemgt funnyItems new
  ArrayListltItemgt()
• for (IteratorltItemgt i items.iterator()
  i.hasNext() )
• Item item i.next()
• if (item.isFunny())
• funnyItems.add(item)
• return items

3
Your code in Groovy!

• enum PeriodType WEEKLY, MONTHLY, QUARTERLY,
  ANNUALLY
• _at_Entity
• class Invoice
• _at_Id
• int id
• _at_OneToMany
• ListltItemgt items
• PeriodType periodType
• public ListltItemgt getFunnyItems()
• ListltItemgt funnyItems new
  ArrayListltItemgt()
• for (IteratorltItemgt i items.iterator()
  i.hasNext() )
• Item item i.next()
• if (item.isFunny())
• funnyItems.add(item)
• return items

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Hello, world

• Legal code, but can omit plumbing
• class Foo
• public static void main(String args)
• System.out.println("Hello, world")

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Hello, world

• Groovy also provides some shortcuts
• System.out.println("Hello, world")

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Hello, world

• Unnecessary punctuation just adds clutter
• System.out.println("Hello, world")

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Hello, world

• System.out.println('Hello, world')

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Why Groovy?

• The power of a dynamic language plus
• JSR 241 Java standard
• Two-way contract
• a Groovy class is a Java class its all
  bytecodes. Groovy and Java can extend each
  others classes.
• Seamless integration with Java annotations,
  generics, enums, familiar syntax.
• The Groovy platform is the Java platform
• the J2SE library, debugging, profiling etc.
• Spring, Hibernate, web services, TestNG

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Some Groovy language features

• Dynamically typed
• Closures
• Everything is an object. No primitives.
• means equals. Really.
• Native syntax for lists, maps, regex
• Operator overriding
• Compact, expressive, readable

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Strings

• greeting 'Hello'
• println "greeting, world"
• println """
• Today's date is new Date().toGMTString()
• Nice day, isn't it?
• """
• greeting "Hello, world"
• greeting7 'w'
• greeting2..4 'llo'

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Closures

• Behavior as objects
• Default argument is it, optional.
• def squareIt return it it
• assert squareIt(5) 25
• 10.times println I will not talk in class
• Captures variables in the lexical scope
• int x 10
• Closure addToX addThis -gt x addThis
• addToX(2)
• assert x 12

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Lists and maps

• mylist 1, 2, 3, 4, 5 // an ArrayList
• assert mylist0 1
• mylist2..3 // deleted 3, 4
• 2,3,4.collect it 2 4, 6, 8
• 1,2,3.find it gt 1 2
• 1,2,3,1,2,3.flatten().unique() 1, 2, 3
• mylist.each doSomethingWith(it)
• mymap a1, b2, c3 // a HashMap
• mymap'a' mymap.a // mymap.get("a")
• mymap'c' 5 // mymap.put("c", 5)

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Ranges and regex

• Ranges
• (1..10).each it -gt println it
• switch (age) case 15..30
• for (i in 1..10)
• 'Hello, world'2..4 'llo'
• Regex
• if ('rain' /\b\wain\b/)
• println '"rain" does rhyme with "Spain"!'

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Operator overriding

• Override operators by overriding methods
• a b a.plus(b)
• ab a.getAt(b)
• a ltlt b a.leftShift(b)
• switch (a) case b ... b.isCase(a)
• a b a.equals(b)
• a lt b a.compareTo(b) lt 0

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Groovy convenience operators

• ? elvis
• Java name name ! null ? name "default"
• Groovy name name ? "default"
• ?. safe dereference. No worry about nulls.
• street user?.address?.street
• . spread dot. Invoke on all items, return list.
• List result invoice.lineItems.total()

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GroovyBeans and JavaBeans

• // Groovy
• class MyBean
• String item
• MyBean b
• new MyBean(itemfoo)
• String val b.item
• b.item bar
• bitem bar

• // Java
• class MyBean
• private String item
• public String getItem()
• public void setItem()
• MyBean b new MyBean()
• b.setItem(foo)
• String val b.getItem()
• b.setItem(bar)

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Why brevity matters Quicksort

• function sort(array) // pseudocode from Wikipedia
• var list less, greater
• if length(array) 1 return array
• select a pivot value pivot from array
• for each x in array
• if x lt pivot then append x to less
• if x gt pivot then append x to greater
• return concatenate(sort(less), pivot,
  sort(greater))
• --------------------------------------------------
  ------
• def sort(list) // Groovy implementation
• if (list.size() lt 1) return list
• def pivot list0
• def less list.findAll it lt pivot
• def same list.findAll it pivot
• def greater list.findAll it gt pivot
• sort(less) same sort(greater)

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Quicksort in Java

• public static void qsort(Comparable c,int
  start,int end)
• if(end lt start) return
• Comparable comp cstart
• int i start,j end 1
• for()
• do i while(iltend
  ci.compareTo(comp)lt0)
• do j-- while(jgtstart
  cj.compareTo(comp)gt0)
• if(j lt i) break
• Comparable tmp ci
• ci cj
• cj tmp
• cstart cj
• cj comp
• qsort(c,start,j-1)
• qsort(c,j1,end)
• public static void qsort(Comparable c)

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Object graph navigation GPaths

• class Invoice List items
• class Item Product product int total()
• class Product String name
• ListltInvoicegt invoices
• // get all product names where item total gt 7000
• List result invoices.items.grepit.total() gt
  7000.product.name
• // Java version
• List result new ArrayList()
• for (IteratorltInvoicegt i invoices.iterator()
  i.hasNext() )
• List items i.next().getItems()
• for (Iterator j items.iterator()
  j.hasNext() )
• Item item (Item) j.next()
• if (item.total() gt 7000)
• result.add(item.getProduct().getName())

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Dynamic Groovy multimethods

• class Equalizer
• boolean equals(Equalizer e) ...
• boolean equals(Object o) ...
• Object obj new Equalizer()
• obj.equals(new Equalizer())

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Dynamic Groovy categories

• // Dynamically add methods to any class
• class PersistenceCategory
• static void save(Object o)
• // save object
• use (PersistenceCategory)
• // all objects now have save() method
• new MyBean().save()

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Dynamic Groovy meta programming

• Change class/object behavior at runtime
• Meta-Object Protocol (MOP)
• You can intercept method calls and property
  accesses
• invokeMethod(...)
• getProperty(...)
• setProperty(...)
• etc

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MarkupBuilder

• builder new groovy.xml.MarkupBuilder()
• builder.numbersAndSquares
• description 'Numbers and squares'
• (3..6).each
• number (value it, square itit)
• ltnumbersAndSquaresgt
• ltdescriptiongtNumbers and squareslt/descriptiongt
• ltnumber value'3' square'9' /gt
• ltnumber value'4' square'16' /gt
• ltnumber value'5' square'25' /gt
• ltnumber value'6' square'36' /gt
• lt/numbersAndSquaresgt

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SwingBuilder

• swing new SwingBuilder()
• frame swing.frame(title 'Hello, world')
• panel(layout new BorderLayout())
• label(text 'Hello, world',
• constraints BorderLayout.CENTER)
• button(text 'Exit',
• constraints BorderLayout.SOUTH,
• actionPerformed
• System.exit(0)
• )
• frame.pack()
• frame.show()

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Domain-specific languages (DSL)

• A DSL is a mini-language aiming at representing
  constructs for a given domain
• Groovy features for DSLs add new
  methods/properties to classes, override
  operators.
• E.g. unit manipulation
• println 30.km/h 2.m/s 2
• println 3 3.mg/L
• println 1/2.s - 2.Hz

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Grails ORM (GORM)

• class Book
• String title
• String author
• Date releaseDate
• book Book.get(id) // let's change the title
• book.title 'War and Peace'
• book.save()
• Book.listOrderByTitle()
• Book.findByReleaseDateBetween(startDate, endDate)

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Groovy warts

• SLOW
• Write critical areas in Java
• Groovy performance rapidly improving
• Poor IDE support
• IntelliJ IDEA's JetGroovy coming along nicely
• Stack dumps are a pain

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Questions/discussion

• Thanks for listening!
• cwong_at_makanasolutions.com