Java · Chapter 15 of 42
Java While Loop
The while loop repeats a block of code as long as a condition remains true. The do-while variant runs the block at least once before checking the condition.
While loops are ideal when the number of iterations isn't known in advance, such as reading input until a sentinel value appears.
Syntax
while (condition) {
}
do {
} while (condition);while loop
The condition is checked before each iteration; if false initially, the loop body never runs.
do-while loop
The condition is checked after the loop body runs, guaranteeing at least one execution.
Example 1 (java)
public class Main {
public static void main(String[] args) {
int i = 0;
while (i < 3) {
System.out.println(i);
i++;
}
}
}Output
0
1
2The loop prints i and increments it while i is less than 3.
Key points
- while checks the condition before each iteration.
- do-while checks the condition after, so it runs at least once.
- Forgetting to update the loop variable causes an infinite loop.
- while loops are good for unknown iteration counts.
💡 Note: Always ensure the loop condition eventually becomes false to avoid infinite loops.