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Java Fundamentals · Loops · Lesson 14 of 22

while and do-while Loops

Concept

while and do-while Loops

while checks its condition before each iteration. do-while runs the loop body at least once before checking, which is useful for menus.

By the end of this lesson
  • Explain the core idea behind while and do-while Loops.
  • Predict output before running a change.
  • Test one realistic and one unusual input.
  • Use the result to make the next decision.
How to study this page
  1. 1. Read one concept.
  2. 2. Change the example.
  3. 3. Run, compare, and explain.
  4. 4. Complete the challenge below.
ExampleRunnable
int count = 0;
while (count < 3) {
    System.out.println(count);
    count++;
}
Try it Yourself »
Self-check before continuing

Without looking at the example, describe what changes when you modify one input in while and do-while Loops. Then reopen the editor and prove your explanation with a small test.

You are ready to continue when you can predict, test, and explain the result.

Your turn

Write a do-while loop that runs exactly once even when its condition starts false.

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Console

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