Java do-while Loop

📘 Premium Read: Access my best content on Medium member-only articles — deep dives into Java, Spring Boot, Microservices, backend architecture, interview preparation, career advice, and industry-standard best practices.

🎓 Top 15 Udemy Courses (80-90% Discount): My Udemy Courses - Ramesh Fadatare — All my Udemy courses are real-time and project oriented courses.

▶️ Subscribe to My YouTube Channel (176K+ subscribers): Java Guides on YouTube

▶️ For AI, ChatGPT, Web, Tech, and Generative AI, subscribe to another channel: Ramesh Fadatare on YouTube


Introduction

The do-while loop in Java is a control flow statement that allows code to be executed repeatedly based on a given boolean condition. Unlike the while loop, the do-while loop guarantees that the code block is executed at least once before the condition is tested. This makes the do-while loop particularly useful for scenarios where you need to ensure that the code block executes at least once.

Table of Contents

  1. What is a do-while Loop?
  2. Syntax of do-while Loop
  3. How do-while Loop Works
  4. Simple do-while Loop Example
  5. Infinite do-while Loop
  6. do-while Loop with a Break Statement
  7. do-while Loop with a Continue Statement
  8. Nested do-while Loop
  9. Using a do-while Loop for Input Validation
  10. Conclusion

What is a do-while Loop?

A do-while loop repeatedly executes a block of code as long as the specified condition evaluates to true. The key difference from a while loop is that the condition is evaluated after the loop body, ensuring that the loop body is executed at least once.

Syntax of do-while Loop

Syntax:

do { // body of loop } while (condition); 
  • condition: A boolean expression that is evaluated after each iteration of the loop.
  • body of loop: The block of code that is executed at least once and as long as the condition is true.

How do-while Loop Works

  1. The loop body is executed.
  2. The condition is evaluated.
  3. If the condition is true, the loop body is executed again.
  4. Steps 2 and 3 are repeated until the condition becomes false.
  5. When the condition is false, the loop terminates, and control moves to the next statement after the loop.

Simple do-while Loop Example

Example:

public class SimpleDoWhileLoop { public static void main(String[] args) { int count = 1; do { System.out.println("Count: " + count); count++; } while (count <= 5); } } 

Explanation: This loop prints the numbers from 1 to 5. The body of the loop is executed first, and then the condition count <= 5 is checked. Since the condition is true, the loop continues to execute until count exceeds 5.

Infinite do-while Loop

An infinite loop occurs when the condition always evaluates to true.

Example:

public class InfiniteDoWhileLoop { public static void main(String[] args) { do { System.out.println("This is an infinite loop"); } while (true); } } 

Explanation: This loop will print "This is an infinite loop" indefinitely because the condition true never changes.

do-while Loop with a Break Statement

The break statement can be used to exit the loop prematurely.

Example:

public class DoWhileWithBreak { public static void main(String[] args) { int count = 1; do { if (count == 5) { break; } System.out.println("Count: " + count); count++; } while (count <= 10); } } 

Explanation: This loop prints numbers from 1 to 4. When count equals 5, the break statement exits the loop.

do-while Loop with a Continue Statement

The continue statement skips the current iteration and moves to the next iteration of the loop.

Example:

public class DoWhileWithContinue { public static void main(String[] args) { int count = 0; do { count++; if (count % 2 == 0) { continue; } System.out.println("Odd number: " + count); } while (count < 10); } } 

Explanation: This loop prints odd numbers from 1 to 9. The continue statement skips the even numbers.

Nested do-while Loop

A nested do-while loop is a do-while loop inside another do-while loop, useful for iterating over multidimensional structures.

Example:

public class NestedDoWhileLoop { public static void main(String[] args) { int i = 1; do { int j = 1; do { System.out.println("i: " + i + ", j: " + j); j++; } while (j <= 3); i++; } while (i <= 3); } } 

Explanation: This loop prints pairs of i and j values, iterating over all combinations of i and j from 1 to 3.

Using a do-while Loop for Input Validation

The do-while loop is often used for validating user input.

Example:

import java.util.Scanner; public class InputValidation { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); int number; do { System.out.print("Enter a positive number: "); number = scanner.nextInt(); if (number <= 0) { System.out.println("Invalid input. Please try again."); } } while (number <= 0); System.out.println("You entered: " + number); scanner.close(); } } 

Explanation: This loop repeatedly prompts the user to enter a positive number until a valid input is provided.

Conclusion

The do-while loop in Java is a powerful control flow statement for performing repeated tasks based on a condition. Unlike the while loop, the do-while loop guarantees that the code block is executed at least once. Understanding how to use the do-while loop effectively, including its variations with break and continue statements, as well as nested loops, is essential for writing robust and efficient Java programs.


Comments

Spring Boot 3 Paid Course Published for Free
on my Java Guides YouTube Channel

Subscribe to my YouTube Channel (165K+ subscribers):
Java Guides Channel

Top 10 My Udemy Courses with Huge Discount:
Udemy Courses - Ramesh Fadatare