Looping in Groovy can be done in several ways. We can use the standard classic Java for loop or use the newer Java for-each loop. But Groovy adds more ways to loop several times and execute a piece of code. Groovy extends the Integer class with the step(), upto() and times() methods. These methods take a closure as a parameter. In the closure we define the piece of code we want to be executed several times.
If we have a List in Groovy we can loop through the items of the list with the each() and eachWithIndex() methods. We also need to pass a closure as parameter to the methods. The closure is then executed for every item in the list.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 | // Result variable for storing loop results.def result = ''// Closure to fill result variable with value.def createResult = { if (!it) { // A bit of Groovy truth: it == 0 is false result = '0' } else { result += it }}// Classic for loop.for (i = 0; i < 5; i++) { createResult(i)}assert '01234' == result// Using int.upto(max).0.upto(4, createResult)assert '01234' == result// Using int.times.5.times(createResult)assert '01234' == result// Using int.step(to, increment).0.step 5, 1, createResultassert '01234' == result// Classic while loop.def z = 0while (z < 5) { createResult(z) z++}assert '01234' == resultdef list = [0, 1, 2, 3, 4]// Classic Java for-each loop.for (int i : list) { createResult(i)}assert '01234' == result// Groovy for-each loop.for (i in list) { createResult(i)}assert '01234' == result// Use each method to loop through list values.list.each(createResult)assert '01234' == result// Ranges are lists as well.(0..4).each(createResult)assert '01234' == result// eachWithIndex can be used with closure: first parameter is value, second is index.result = ''list.eachWithIndex { listValue, index -> result += "$index$listValue" }assert '0011223344' == result |
