Pears of Wisdom - Groovy Fundamentals

Alex Poiry
Note by Alex Poiry, updated more than 1 year ago
Alex Poiry
Created by Alex Poiry about 3 years ago
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The basics of Groovy

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Page 1

High Level Groovy Concepts TODO   Basic Syntax System.out.println("Hello Groovy") ;  is the same as, println("Hello Groovy");   is the same as, println("Hello Groovy")   is the same as, println "Hello Groovy" Groovy will let you write Java-like syntax, but really only needs basic ruby-like syntax.   def  :  used to define variables   String Interpolation is done like this: def greeting = "Hello, " println "$greeting" + "Groovy"   Adding the { } characters tell string interpolation to apply to a whole expression or variable, like this: def greeting = "Hello, " def who =  ["Groovy", "World"] println "$greeting" + "${who[0]}"   Idiomatic Groovy uses double quotes for string interpolation only, otherwise use a single quote.   Looping def greeting = "Hello, " def who =  ["Groovy", "World"] for (name in who) {   println "$greeting" + "$name" }   Ranges def numbers = 1..10   :    This creates a collection, it also works with things like letters and enums println numbers.from    :    This equals 1 println numbers.to     :     This equals 10   Functions def camelCaseName(val) {   "Sweet" } Note that the last line in the method is returned by default. You can explicitly call return if you need multiple return points.   Closures def myClosure = { println "A closure" } The each method can accept a closure Each has an implicit reference to the current item in the iteration, which is 'it', like this: def who =  ["Groovy", "World"] who.each({ println it }) This will print Groovy, then World If you have multiple iterators you can explicitly define the current iteration like this: who.each({ name -> println name })   Dump & Inspect You can print out a lot of information about an object by calling dump.  This should provide you the object type, its inheritance hierarchy, as well as its members There is also a method called inspect.  Developers are expected to override inspect with useful information.  If they haven't don that, it defaults to the toString() method for the object.   With This is a helper method on objects called with.  It accepts a closure and prevents you from having to continually re-type a variable name whose dot methods you are accessing, like this: data.with {   println item   println thing } AS OPPOSED TO println data.item println data.thing   Groovy Truthfulness Any not null value evaluates to true on a boolean comparison, like this: if (!value) AS OPPOSED TO if (value == null)   Categories TODO

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Some Basic Activities   def file = new File('../path/to/file.xml') def slurper = new XmlSlurper() def data = slurper.parse(file) println data.elementName println data.@attribute println data.elementA.elementB println data.elementA.elementB.@otherAttr   XmlSlurper will also dynamically determine the type of XML object and try to convert it, so you can run collection methods on XML arrays, etc.

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