Loops

Groovy supports Java's loops and adds shorter ones based on methods.

for-in

for (fruit in ['apple', 'banana', 'cherry']) {
    println fruit
}

for (i in 1..3) {
    print "$i "
}
println()

apple
banana
cherry
1 2 3

for (x in collection) loops over any list, range, map, string, or array. println() with empty parentheses prints just a new line.

Counting loops

3.times { print "Hip! " }
println 'Hooray!'

1.upto(4) { print "$it " }
println()

10.downto(7) { print "$it " }
println()

0.step(10, 3) { print "$it " }
println()

for (int i = 0; i < 3; i++) {
    print "i=$i "
}
println()

Hip! Hip! Hip! Hooray!
1 2 3 4
10 9 8 7
0 3 6 9
i=0 i=1 i=2

times, upto, downto, and step take a closure — the block in braces — and call it with each number as it. The classic Java for loop works too.

while

def balance = 1000
def years = 0
while (balance < 2000) {
    balance *= 1.07
    years++
}
println "Doubled after $years years: ${balance.setScale(2, java.math.RoundingMode.HALF_UP)}"

Doubled after 11 years: 2104.85

Groovy also supports Java's do { ... } while (condition) loop, which runs its body at least once.

break and continue

for (n in 1..10) {
    if (n % 2 == 0) continue    // skip even numbers
    if (n > 7) break            // stop the loop
    print "$n "
}
println()

1 3 5 7

Common mistakes

• Using break or continue inside each { } or times { } — they are closures, not loops, so break is a compile error there and return only skips to the next item. When you need to stop early, use for (x in ...), or find/any (Level 2).

Practice

Print the multiplication table for 7, from 7 x 1 = 7 to 7 x 5 = 35.

1.upto(5) { i ->
    println "7 x $i = ${7 * i}"
}

7 x 1 = 7
7 x 2 = 14
7 x 3 = 21
7 x 4 = 28
7 x 5 = 35