Java while Loop Explained with Examples

Java - While Loop

Chapter Exercises Videos Discussion

Q1. How does a while loop decide whether to execute its block of code ?

A while loop is an entry-controlled loop, which means the condition is checked before the loop body executes.

If the condition evaluates to true, the loop body executes.

If the condition evaluates to false, the loop body is skipped and execution moves to the next statement after the loop.

Because of this behavior, a while loop may execute zero or more times, depending on the condition.

Q2. What happens if the loop control varibale is not updated inside a while loop ?

If the loop control variable is not updated inside the while loop, the loop may become an infinite loop.

Example

int i = 1;

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

In this case, the condition i <= 5 always remains true because i is never incremented. As a result, the loop runs endlessly.

To avoid infinite loops, the loop variable must be properly updated inside the loop body.

Q3. How should a loop variable be initialized and updated in a while loop ?

In a while loop:

The loop variable should be initialized before the loop starts.

The loop variable should be updated inside the loop body.

Example

int num = 10;

while (num >= 1) {
    System.out.println(num);
    num--;
}

This structure ensures

The condition is checked correctly

The loop progresses toward termination

The loop ends at the expected point

Q4. Which loop should be used if the code must execute at least once ?

A do-while loop should be used when the loop body must execute at least once, regardless of the condition.

This is because

do-while executes the body first

The condition is checked after execution

Unlike a while loop, a do-while loop guarantees one execution even if the condition is initially false.

Q5. How is a while loop useful in real world scenarios like login attempts ?

A while loop is useful when the number of iterations is not fixed and depends on a condition.

For example, in a login system

The loop can continue while the number of attempts is less than a limit

The loop stops when either the user logs in successfully or the maximum attempts are reached

This makes while loops ideal for:

Input validation

Retry mechanisms

Condition-based repetition