while Loops

A while loop repeats as long as its condition is true. Unlike a for loop, it does not collect initialization and updating in the header. Put the initial state before the loop and make the change that moves it toward stopping visible in the body. A loop whose state never changes can run forever.

Use for when a fixed sequence or count is the clearest plan. Use while when the next step depends on current progress: save until a goal is reached, or process input until it ends. The condition is checked before the body, so a goal already met means zero iterations. Keep those boundary cases in your tests.

State a stopping argument

Before pressing Run, name the value that changes and the direction it moves. For this savings example, a positive addition moves saved upward toward the goal. If the addition were zero or negative, that argument would fail. In an editor, Stop can end a runaway program, but a well-designed loop should also terminate for its intended inputs.

public class Main {
    public static void main(String[] args) {
        int saved = 0;
        int weeks = 0;

        while (saved < 50) {
            saved += 15;
            weeks++;
        }

        System.out.println(saved);
        System.out.println(weeks);
    }
}

60
4

The saved values are 15, 30, 45 and 60. Reaching at least 50 does not mean landing exactly on 50. Using saved != 50 would never stop for increments of 15.

public class Main {
    public static void main(String[] args) {
        int saved = 0;
        int weeks = 0;

        while (saved < 200 && weeks < 3) {
            saved += 15;
            weeks++;
        }

        System.out.println(saved);
        System.out.println(saved >= 200);
    }
}

45
false

The step limit bounds this attempt but does not prove success. Report the unmet goal honestly. Distinguish a stopping condition from a success condition when there is more than one way to stop.

public class Main {
    public static void main(String[] args) {
        int total = 0;

        for (int value = 1; value <= 5; value++) {
            if (value == 3) {
                continue;
            }

            total += value;
        }

        System.out.println(total);
    }
}

12

continue skips the rest of this iteration; the for-loop update still happens. Replace continue with break: the loop ends entirely and the total becomes 3. In a while loop, a continue can skip your own update, so keep updates visible.

Your turn

public class Main {
    public static void main(String[] args) {
        int completed = 0;
        int sessions = 0;
        int target = 55;
        // Repeat until the target is met.
    }
}

public class Main {
    public static void main(String[] args) {
        int completed = 0;
        int sessions = 0;
        int target = 55;

        while (completed < target) {
            completed += 20;
            sessions++;
        }

        System.out.println(completed);
        System.out.println(sessions);
    }
}

60
3

Change it and explain

For targets 1, 20, 21 and 60, predict the session count before running. Add an upper bound of two sessions, then print whether the target was actually reached. Explain which condition stopped the loop for target=55.

If an experiment runs too long, press Stop, inspect the condition and update, and reset if needed. The browser’s safety limit is not a substitute for a termination argument. You should be able to explain why your intended inputs finish without relying on a hidden timeout.