Java Do-While Loop - Syntax, Flowchart and Examples

⏱️ 7 min read • Beginner Level • Lesson 27

The do-while loop in Java is used to execute a block of code repeatedly as long as a given condition is true. Unlike the while loop, the do-while loop checks the condition after executing the loop body.

This means a do-while loop executes the loop body at least once, even if the condition is false at the beginning. Before learning this topic, you should understand Java while loop, Java operators, and Java variables.

What is Do-While Loop in Java?

A do-while loop is an exit-controlled loop. It first executes the loop body and then checks the condition. If the condition is true, the loop repeats. If the condition is false, the loop stops.

Syntax of do-while Loop

The syntax of a do-while loop is slightly different from a while loop because the condition appears at the end.

initialization;

do {
    // loop body
    update;
} while (condition);

Flowchart of do-while Loop

The following diagram shows how a do-while loop works. Java executes the loop body first and then checks the condition.

Real-World Uses of do-while Loop

Java do-while Loop Example

The following program prints Hello five times using a do-while loop.

public class DoWhileDemo {
    public static void main(String[] args) {
        int i = 1;

        do {
            System.out.println(i + ". Hello");
            i++;
        } while (i <= 5);
    }
}

Output:

1. Hello
2. Hello
3. Hello
4. Hello
5. Hello

Why do-while Loop Executes At Least Once?

In a do-while loop, the condition is checked after the loop body. Therefore, even if the condition is false from the beginning, the loop body still runs once.

public class DoWhileRunsOnce {
    public static void main(String[] args) {
        int i = 10;

        do {
            System.out.println("This runs once");
        } while (i < 5);
    }
}

Output:

This runs once

Example: Sum of First 5 Numbers

This example calculates the sum of numbers from 1 to 5 using a do-while loop.

public class SumDoWhileLoop {
    public static void main(String[] args) {
        int i = 1;
        int sum = 0;

        do {
            sum = sum + i;
            i++;
        } while (i <= 5);

        System.out.println("Sum = " + sum);
    }
}

Output:

Sum = 15

Example: Menu using do-while Loop

The do-while loop is commonly used in menu-driven programs because the menu should be displayed at least once.

import java.util.Scanner;

public class MenuDoWhileExample {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int choice;

        do {
            System.out.println("MENU");
            System.out.println("1. Say Hello");
            System.out.println("2. Exit");
            System.out.print("Enter your choice: ");

            choice = sc.nextInt();

            if (choice == 1) {
                System.out.println("Hello User!");
            } else if (choice == 2) {
                System.out.println("Goodbye!");
            } else {
                System.out.println("Invalid choice!");
            }

        } while (choice != 2);

        sc.close();
    }
}

Sample Output:

MENU
1. Say Hello
2. Exit
Enter your choice: 1
Hello User!
MENU
1. Say Hello
2. Exit
Enter your choice: 2
Goodbye!

Difference Between while Loop and do-while Loop

Common Mistakes in do-while Loop

Interview Questions ⭐

🧠 Test your understanding with a quick quiz

int i = 10;
do {
    System.out.println("Hello");
} while (i < 5);

int i = 1;
do {
    System.out.println(i);
    i++;
} while (i <= 3);

🎉 Great job! Continue learning Java step by step.