Note - groovy basic

2018, May 10    

Apache Groovy is a powerful, optionally typed and dynamic language, with static-typing and static compilation capabilities, for the Java platform aimed at improving developer productivity thanks to a concise, familiar and easy to learn syntax. It integrates smoothly with any Java program, and immediately delivers to your application powerful features, including scripting capabilities, Domain-Specific Language authoring, runtime and compile-time meta-programming and functional programming.

Closures

Parameters

def power = { int x, int y ->
 return Math.pow(x, y)
}

you can also skip the type of parameters

def say = { what ->
 println what
}

closure can accept one parameter which is available by the name it inside of the closure

def say = { println it }

Optional Return

the last statement of a method block (or closure) is returned implicitly

Passing Closures around

def transform = { str, transformation ->
 transformation(str)
}
println transform("Hello World", { it.toUpperCase() })

Closing of variables

def createGreeter = { name ->
 return {
 def day = new Date().getDay()
 if (day == 0 || day == 6) {
 println "Nice Weekend, $name"
 } else {
 println "Hello, $name"
 }
 }
}

def greetWorld = createGreeter("World")

greetWorld()

Implicit Truthy

  • Strings: If empty false, otherwise true
  • Collections and Maps are true if they are not empty
  • All non-zero numbers are true
  • Matchers (from a regular expression check) are true if they found at least one match
  • Iterators with further elements are true
  • Object references are true if they aren’t null (you can define a custom truthy logic for your classes by implementing the boolean asBoolean() method)

New and noteworthy Operators

Safe Navigation Operator “?”

if(company.getContact()?.getAddress()?.getCountry() == Country.NEW_ZEALAND) { ... }

Ranges

  • 1..10 - an inclusive Range
  • 1..<10 - f an exclusive Range
  • ‘a’..’x’ – Ranges can also consist of characters
  • 10..1 – Ranges can also be in descending order
  • ‘x’..’a’ – Ranges can also consist of characters and be in descending order.

Regular Expressions

def matcher = "The Hitchhiker's Guide to the Galaxy" =~ /Galaxy/
if (matcher) {
 println "Found the word 'Galaxy'"
}

if You define a string inside two slashes /../, that you don’t need to escape a backslash character,

Traits

Traits can be seen as interfaces carrying both default implementations and state.

  • Traits may implement interfaces
  • A trait may define properties
  • Traits may extend another trait, using the extends keyword.
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# groovy