Loops

Java has three main loop forms: the counting for, the condition while, and the collection-walking enhanced for (for-each).

Syntax

for (int i = 0; i < 5; i++) {
    System.out.println(i);
}

int i = 0;
while (i < 5) {
    System.out.println(i);
    i++;
}

int[] nums = {10, 20, 30};
for (int n : nums) {
    System.out.println(n);
}

Example

for (int i = 1; i <= 3; i++) {
    System.out.println("Count: " + i);
}

Expected output

Count: 1
Count: 2
Count: 3

Common mistakes

• Writing i <= nums.length instead of i < nums.length when indexing an array by hand — this reads one past the end and throws ArrayIndexOutOfBoundsException.
• An infinite loop from forgetting to update the loop variable inside a while body.

Practice

Print the numbers 1 through 5 using a for loop.

for (int i = 1; i <= 5; i++) {
    System.out.println(i);
}