44. The while loop

The while loop will repeat a block of code whilst its condition is true:

while (<condition>) {
	//statements
}

while loops feature the following:

• <condition> can be a value or expression - the loop will only iterate if <condition> is true.
• The while loop syntax does not manage an iterator variable - you must do this yourself
  • It’s very easy to create an infinite while loop if you’re not paying attention

The example below uses a common approach for while loops and sets a flag to indicate when the desired state has been reached and the loop can stop:

def flag = false
def num = 0

while (!flag) {
    num++
    if (num**2 == 64) {
        flag = true
    }
}

println "The square root of 64 is $num"

The code above will increment num by 1 each iteration and test to see if num^2 is equal to 64. Once the correct num is reached, flag is change to true and the while condition now resolves to false - indicating that the while loop should run the next iteration.

The while loop can also be used to create an infinite loop: while(true) {}

There is no do...while loop

Unlike Java, Groovy does not have a do...while loop¹. Don’t be sad.