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diff --git a/groovy.html.markdown b/groovy.html.markdown new file mode 100644 index 00000000..492c1ba2 --- /dev/null +++ b/groovy.html.markdown @@ -0,0 +1,432 @@ +--- +language: Groovy +filename: learngroovy.groovy +contributors: + - ["Roberto Pérez Alcolea", "http://github.com/rpalcolea"] +filename: learngroovy.groovy +--- + +Groovy - A dynamic language for the Java platform [Read more here.](http://www.groovy-lang.org/) + +```groovy + +/* + Set yourself up: + + 1) Install GVM - http://gvmtool.net/ + 2) Install Groovy: gvm install groovy + 3) Start the groovy console by typing: groovyConsole + +*/ + +// Single line comments start with two forward slashes +/* +Multi line comments look like this. +*/ + +// Hello World +println "Hello world!" + +/* + Variables: + + You can assign values to variables for later use +*/ + +def x = 1 +println x + +x = new java.util.Date() +println x + +x = -3.1499392 +println x + +x = false +println x + +x = "Groovy!" +println x + +/* + Collections and maps +*/ + +//Creating an empty list +def technologies = [] + +/*** Adding a elements to the list ***/ + +// As with Java +technologies.add("Grails") + +// Left shift adds, and returns the list +technologies << "Groovy" + +// Add multiple elements +technologies.addAll(["Gradle","Griffon"]) + +/*** Removing elements from the list ***/ + +// As with Java +technologies.remove("Griffon") + +// Subtraction works also +technologies = technologies - 'Grails' + +/*** Iterating Lists ***/ + +// Iterate over elements of a list +technologies.each { println "Technology: $it"} +technologies.eachWithIndex { it, i -> println "$i: $it"} + +/*** Checking List contents ***/ + +//Evaluate if a list contains element(s) (boolean) +contained = technologies.contains( 'Groovy' ) + +// Or +contained = 'Groovy' in technologies + +// Check for multiple contents +technologies.containsAll(['Groovy','Grails']) + +/*** Sorting Lists ***/ + +// Sort a list (mutates original list) +technologies.sort() + +// To sort without mutating original, you can do: +sortedTechnologies = technologies.sort( false ) + +/*** Manipulating Lists ***/e + +//Replace all elements in the list +Collections.replaceAll(technologies, 'Gradle', 'gradle') + +//Shuffle a list +Collections.shuffle(technologies, new Random()) + +//Clear a list +technologies.clear() + +//Creating an empty map +def devMap = [:] + +//Add values +devMap = ['name':'Roberto', 'framework':'Grails', 'language':'Groovy'] +devMap.put('lastName','Perez') + +//Iterate over elements of a map +devMap.each { println "$it.key: $it.value" } +devMap.eachWithIndex { it, i -> println "$i: $it"} + +//Evaluate if a map contains a key +assert devMap.containsKey('name') + +//Evaluate if a map contains a value +assert devMap.containsValue('Roberto') + +//Get the keys of a map +println devMap.keySet() + +//Get the values of a map +println devMap.values() + +/* + Groovy Beans + + GroovyBeans are JavaBeans but using a much simpler syntax + + When Groovy is compiled to bytecode, the following rules are used. + + * If the name is declared with an access modifier (public, private or + protected) then a field is generated. + + * A name declared with no access modifier generates a private field with + public getter and setter (i.e. a property). + + * If a property is declared final the private field is created final and no + setter is generated. + + * You can declare a property and also declare your own getter or setter. + + * You can declare a property and a field of the same name, the property will + use that field then. + + * If you want a private or protected property you have to provide your own + getter and setter which must be declared private or protected. + + * If you access a property from within the class the property is defined in + at compile time with implicit or explicit this (for example this.foo, or + simply foo), Groovy will access the field directly instead of going though + the getter and setter. + + * If you access a property that does not exist using the explicit or + implicit foo, then Groovy will access the property through the meta class, + which may fail at runtime. + +*/ + +class Foo { + // read only property + final String name = "Roberto" + + // read only property with public getter and protected setter + String language + protected void setLanguage(String language) { this.language = language } + + // dynamically typed property + def lastName +} + +/* + Logical Branching and Looping +*/ + +//Groovy supports the usual if - else syntax +def x = 3 + +if(x==1) { + println "One" +} else if(x==2) { + println "Two" +} else { + println "X greater than Two" +} + +//Groovy also supports the ternary operator: +def y = 10 +def x = (y > 1) ? "worked" : "failed" +assert x == "worked" + +//Groovy supports 'The Elvis Operator' too! +//Instead of using the ternary operator: + +displayName = user.name ? user.name : 'Anonymous' + +//We can write it: +displayName = user.name ?: 'Anonymous' + +//For loop +//Iterate over a range +def x = 0 +for (i in 0 .. 30) { + x += i +} + +//Iterate over a list +x = 0 +for( i in [5,3,2,1] ) { + x += i +} + +//Iterate over an array +array = (0..20).toArray() +x = 0 +for (i in array) { + x += i +} + +//Iterate over a map +def map = ['name':'Roberto', 'framework':'Grails', 'language':'Groovy'] +x = 0 +for ( e in map ) { + x += e.value +} + +/* + Operators + + Operator Overloading for a list of the common operators that Groovy supports: + http://www.groovy-lang.org/operators.html#Operator-Overloading + + Helpful groovy operators +*/ +//Spread operator: invoke an action on all items of an aggregate object. +def technologies = ['Groovy','Grails','Gradle'] +technologies*.toUpperCase() // = to technologies.collect { it?.toUpperCase() } + +//Safe navigation operator: used to avoid a NullPointerException. +def user = User.get(1) +def username = user?.username + + +/* + Closures + A Groovy Closure is like a "code block" or a method pointer. It is a piece of + code that is defined and then executed at a later point. + + More info at: http://www.groovy-lang.org/closures.html +*/ +//Example: +def clos = { println "Hello World!" } + +println "Executing the Closure:" +clos() + +//Passing parameters to a closure +def sum = { a, b -> println a+b } +sum(2,4) + +//Closures may refer to variables not listed in their parameter list. +def x = 5 +def multiplyBy = { num -> num * x } +println multiplyBy(10) + +// If you have a Closure that takes a single argument, you may omit the +// parameter definition of the Closure +def clos = { print it } +clos( "hi" ) + +/* + Groovy can memorize closure results [1][2][3] +*/ +def cl = {a, b -> + sleep(3000) // simulate some time consuming processing + a + b +} + +mem = cl.memoize() + +def callClosure(a, b) { + def start = System.currentTimeMillis() + mem(a, b) + println "Inputs(a = $a, b = $b) - took ${System.currentTimeMillis() - start} msecs." +} + +callClosure(1, 2) +callClosure(1, 2) +callClosure(2, 3) +callClosure(2, 3) +callClosure(3, 4) +callClosure(3, 4) +callClosure(1, 2) +callClosure(2, 3) +callClosure(3, 4) + +/* + Expando + + The Expando class is a dynamic bean so we can add properties and we can add + closures as methods to an instance of this class + + http://mrhaki.blogspot.mx/2009/10/groovy-goodness-expando-as-dynamic-bean.html +*/ + def user = new Expando(name:"Roberto") + assert 'Roberto' == user.name + + user.lastName = 'Pérez' + assert 'Pérez' == user.lastName + + user.showInfo = { out -> + out << "Name: $name" + out << ", Last name: $lastName" + } + + def sw = new StringWriter() + println user.showInfo(sw) + + +/* + Metaprogramming (MOP) +*/ + +//Using ExpandoMetaClass to add behaviour +String.metaClass.testAdd = { + println "we added this" +} + +String x = "test" +x?.testAdd() + +//Intercepting method calls +class Test implements GroovyInterceptable { + def sum(Integer x, Integer y) { x + y } + + def invokeMethod(String name, args) { + System.out.println "Invoke method $name with args: $args" + } +} + +def test = new Test() +test?.sum(2,3) +test?.multiply(2,3) + +//Groovy supports propertyMissing for dealing with property resolution attempts. +class Foo { + def propertyMissing(String name) { name } +} +def f = new Foo() + +assertEquals "boo", f.boo + +/* + TypeChecked and CompileStatic + Groovy, by nature, is and will always be a dynamic language but it supports + typechecked and compilestatic + + More info: http://www.infoq.com/articles/new-groovy-20 +*/ +//TypeChecked +import groovy.transform.TypeChecked + +void testMethod() {} + +@TypeChecked +void test() { + testMeethod() + + def name = "Roberto" + + println naameee + +} + +//Another example: +import groovy.transform.TypeChecked + +@TypeChecked +Integer test() { + Integer num = "1" + + Integer[] numbers = [1,2,3,4] + + Date date = numbers[1] + + return "Test" + +} + +//CompileStatic example: +import groovy.transform.CompileStatic + +@CompileStatic +int sum(int x, int y) { + x + y +} + +assert sum(2,5) == 7 + + +``` + +## Further resources + +[Groovy documentation](http://www.groovy-lang.org/documentation.html) + +[Groovy web console](http://groovyconsole.appspot.com/) + +Join a [Groovy user group](http://www.groovy-lang.org/usergroups.html) + +## Books + +* [Groovy Goodness] (https://leanpub.com/groovy-goodness-notebook) + +* [Groovy in Action] (http://manning.com/koenig2/) + +* [Programming Groovy 2: Dynamic Productivity for the Java Developer] (http://shop.oreilly.com/product/9781937785307.do) + +[1] http://roshandawrani.wordpress.com/2010/10/18/groovy-new-feature-closures-can-now-memorize-their-results/ +[2] http://www.solutionsiq.com/resources/agileiq-blog/bid/72880/Programming-with-Groovy-Trampoline-and-Memoize +[3] http://mrhaki.blogspot.mx/2011/05/groovy-goodness-cache-closure-results.html |