How to use for and while loops

Use a for loop

A for loop groups initialization, condition, and update. This example prints zero through four.

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

Use a while loop

A while loop tests before every iteration. Update the controlling value so the loop can finish.

int count = 3;
while (count > 0) {
    System.out.println(count);
    count--;
}

Use do-while

A do-while loop tests after its body, so the body always runs at least once.

int choice = 1;
do {
    System.out.println("Choice: " + choice);
    choice++;
} while (choice <= 3);

Prevent endless loops

• Make the loop condition become false eventually.
• Check boundary operators such as < versus <=.
• Trace the loop variable by hand when output is unexpected.