Loop Types: while vs do/while vs for

Three ways to repeat code in Java -- see them execute side by side

Sum 1 to N, where N = 5

Ready -- press Step or Play

while loop

int i = 1, sum = 0;
while (i <= N) {
sum += i;
i++;
}

sum

Waiting...

int i = 1, sum = 0

i <= N ?

sum += i

i++

↩ back to condition

Done

do/while loop

int i = 1, sum = 0;
do {
sum += i;
i++;
} while (i <= N);

sum

Waiting...

int i = 1, sum = 0

sum += i

i++

i <= N ?

↩ back to body

Done

for loop

for (int i = 1; i <= N; i++) {
sum += i;
}
// sum declared before loop
int sum = 0;

sum

Waiting...

int i = 1, sum = 0

i <= N ?

sum += i

i++

↩ back to condition

Done

Key Differences

Feature	while	do/while	for
Checks condition	Before body	After body	Before body
Minimum runs	0	1	0
Best for	Unknown iterations	At least once	Known count

What if the condition is false from the start? (N = 0)

Set the slider to 0 and step through to see the difference, or press the button below for a quick demo.

Tip: Use for when you know how many times to loop. Use while when you're waiting for a condition. Use do/while when you need at least one iteration (rare in practice).

Color key: initialization | condition | body | update

← Object Lifecycle break vs continue →