do-while Loop — Java

Java do-while Loop

What is a do-while Loop?

A do-while loop is a close cousin of the while loop, with one important twist: it checks its condition AFTER running the loop body, not before. That means the body of a do-while loop always executes at least once, no matter what the condition evaluates to.

Basic Syntax

Java

do {
    // code to repeat
} while (condition);

Warning

Don't forget the semicolon after while (condition) — it's easy to drop since a regular while loop doesn't end with one. Leaving it off is a compile error.

Key Difference From while

In a while loop, the condition is checked BEFORE the first iteration, so the body might never run. In a do-while loop, the body runs first, and the condition is only checked afterward, to decide whether to run it AGAIN.

while: body may never run

Java

int count = 10;
while (count < 5) {
    System.out.println("while: " + count);
    count++;
}
System.out.println("while loop finished");

while loop finished

do-while: body always runs once

Java

int count = 10;
do {
    System.out.println("do-while: " + count);
    count++;
} while (count < 5);
System.out.println("do-while loop finished");

do-while: 10
do-while loop finished

Note

Even though count starts at 10 and the condition (count < 5) is false from the very beginning, the do-while body still runs exactly once before the condition is ever checked.

A Simple Counting Example

Java

int i = 1;
do {
    System.out.println("Count: " + i);
    i++;
} while (i <= 5);

Count: 1
Count: 2
Count: 3
Count: 4
Count: 5

Practical Use Case: A Menu Loop

do-while is the natural fit whenever you want to show something to the user AT LEAST ONCE before deciding whether to repeat — a text menu is the textbook example. You want the menu to display at least one time, then keep redisplaying until the user chooses to exit.

Java

import java.util.Scanner;

Scanner scanner = new Scanner(System.in);
int choice;

do {
    System.out.println("1. View Balance");
    System.out.println("2. Deposit");
    System.out.println("3. Withdraw");
    System.out.println("4. Exit");
    System.out.print("Choose an option: ");
    choice = scanner.nextInt();

    switch (choice) {
        case 1 -> System.out.println("Balance: $500");
        case 2 -> System.out.println("Deposit successful");
        case 3 -> System.out.println("Withdrawal successful");
        case 4 -> System.out.println("Goodbye!");
        default -> System.out.println("Invalid option, try again.");
    }
} while (choice != 4);

Note

The menu prints at least once even before the user has made any choice — that's exactly the behavior a do-while loop gives you for free.

while vs do-while

Aspect	while	do-while
Condition checked	Before the body runs	After the body runs
Minimum executions	0 (may never run)	1 (always runs at least once)
Ends with semicolon	No	Yes — while (condition);
Typical use	Sentinel loops, input validation	Menus, "run once then repeat" logic

Practice Exercises

Write a do-while loop that asks the user to guess a number until they get it right.
Build a simple text-based menu using do-while with at least three options.
Use a do-while loop to print numbers 1 to 5, then modify it so the condition is initially false and observe that it still runs once.