Java · Theory

Java While Loop

Theory

20/270

Java While Loop

while repeats as long as a condition stays true. Check first. If the condition is already false, the body never runs. Shape: while (condition) { body }.

Something inside the body must move toward stopping — i++, or a new input — or the loop never ends. while is good when the count is not known: keep reading until the user types stop.

for is better with a counter. while is better with “until this becomes false”. Contrast with do-while: while can run zero times; do-while runs at least once.

Let's take this on the board with one tiny Main class — no extra files. Java While Loop — output: 1 then 2 then 3. i starts at 1. When i becomes 4, i<=3 is false — loop stops. Start from main, go line by line, and stop at each print. That output is the proof for While Loop.

Diagram

check first ── false → stop
         │ true
         ▼
       body
         │
         └── check again

Exam tip

Contrast while (check first) vs do-while (body first).

Example

// Java While Loop — prints 1, 2, 3
public class Main {
  public static void main(String[] args) {
    int i = 1;
    while (i <= 3) {
      System.out.println(i);
      i++;
    }
  }
}

Java While Loop — output: 1 then 2 then 3. i starts at 1. When i becomes 4, i<=3 is false — loop stops.

Short notes

Defwhile repeats while the condition is true. Check happens first.
RuleUpdate the variable inside the body or it loops forever.
Rememberwhile can run 0 times. do-while runs at least once.
UseRead until stop, wait until a goal is met.

Java · Theory

Java While Loop

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Theory

20/270

Java While Loop

while repeats as long as a condition stays true. Check first. If the condition is already false, the body never runs. Shape: while (condition) { body }.

Something inside the body must move toward stopping — i++, or a new input — or the loop never ends. while is good when the count is not known: keep reading until the user types stop.

for is better with a counter. while is better with “until this becomes false”. Contrast with do-while: while can run zero times; do-while runs at least once.

Diagram

check first ── false → stop
         │ true
         ▼
       body
         │
         └── check again

Exam tip

Contrast while (check first) vs do-while (body first).

Example

// Java While Loop — prints 1, 2, 3
public class Main {
  public static void main(String[] args) {
    int i = 1;
    while (i <= 3) {
      System.out.println(i);
      i++;
    }
  }
}

Java While Loop — output: 1 then 2 then 3. i starts at 1. When i becomes 4, i<=3 is false — loop stops.

Short notes

Defwhile repeats while the condition is true. Check happens first.
RuleUpdate the variable inside the body or it loops forever.
Rememberwhile can run 0 times. do-while runs at least once.
UseRead until stop, wait until a goal is met.

Java While Loop

Example

Short notes

Questions

Java While Loop

Example

Short notes

Questions