Essential Concepts

Assert is a way to evaluate an expresion if it is true

assert 1 == 1
def x = 1; assert x == 1
def y = 2; assert y == 2
assert ('text'*3<<'hello').size() == 4*3+5

Everything in Groovy is an object

int a = 1
double b = 2.0
float c = 3.0
char d = 'a'
boolean e = true

println a.class
println b.class
println c.class
println d.class
println e.class


class java.lang.Integer
class java.lang.Double
class java.lang.Float
class java.lang.Character
class java.lang.Boolean

Groovy automatically import this packages:

import java.lang.*
import java.util.*
import java.net.*
import java.io.*
import groovy.lang.*
import groovy.util.*

And this classes:

import java.math.BigInteger
import java.math.BigDecimal


The findXXX() methods take a closure and if an element matches the condition defined in the closure we get a result. We can also use the any() method to verify if at least one element applies to the closure condition, or we use the every() method to everify all elements that confirm to the closure condition. Both the any() and every() method return a Boolean value.

assert 'abcde'.find{ it > 'b' } == 'c'
assert 'abcde'.findAll{ it > 'b' } == ['c', 'd', 'e']
assert 'abcde'.findIndexOf{ it > 'c' } == 3
assert 'abcde'.every{ it < 'g' }
assert 'abcde'.any{ it > 'c' }
assert 'josdem'.replace('o','0') == 'j0sdem'
assert 'AbcdE'.equalsIgnoreCase('aBCDe')


In Groovy we use the =~ operator (find operator) to create a new matcher object. We can use a second operator, ==~ (match operator), to do exact matches. With this operator the matches() method is invoked on the matcher object. The result is a Boolean value.

def matcher = ('groovy' =~ /[a-z]*/)
assert matcher instanceof java.util.regex.Matcher
assert matcher[0] == 'groovy'

def match = ('groovy' ==~ /[a-z]*/)
assert match instanceof Boolean

def matcher =  'Groovy rocks!' =~ /Groovy/
assert matcher[0] == 'Groovy'

assert 'Groovy rocks!' ==~ /Groovy rocks!/
assert 'Groovy rocks!' ==~ /Groovy.*/

String uuid = "TimbreFiscalDigital version=\"1.0\" UUID=\"84918EDD-17BE-4726-A217-8430B97B0BD9\" FechaTimbrado=\"2016-04-05T14:48:40\" selloCFD=\"Rgk8ofr4Ud35k2=\" selloSAT=\"z9DT2PLPg9Kg="
def matcher = uuid =~ /[a-zA-Z0-9]{8}-[a-zA-Z0-9]{4}-[a-zA-Z0-9]{4}-[a-zA-Z0-9]{4}-[a-zA-Z0-9]{12}/
assert matcher[0] == "84918EDD-17BE-4726-A217-8430B97B0BD9"

Dynamic Typing

A language is dynamically typed if the type of a variable is interpreted at runtime.

def var
var = 1; assert var.class == java.lang.Integer
var = 2f; assert var.class == java.lang.Float
var = 3d; assert var.class == java.lang.Double
var = 4g; assert var.class == java.math.BigInteger
var = 'Groovy'; assert var.class == java.lang.String
var = true; assert var.class == java.lang.Boolean

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