Java Do While Loop

Do..While loop in java is similar to while loop except do-while loop evaluates its condition expression after the execution of loop code block. Do..While loop in java is used to execute a block of code multiple times.

Do while loop ensures that that code block inside do-while body will execute atleast once. As the condition expression check is after do-while loop code block, it first execute it's code block and then decide whether to iterate again or not.

By the end of this tutorial, you'll have a solid understanding of how to effectively leverage the do-while loop in your Java programs.

Understanding the Basic Syntax of do-while Loop

do {
    // do while loop code block
} while(condition);
  • statement(s); : This block of code is executed at least once.

  • condition : The loop continues to execute as long as this boolean expression evaluates to true. If the condition becomes false, the loop terminates.

Control flow of do-while loop

condition expression is a boolean expression which gets evaluated every time after loop code block. Here is the description of do..while loop control flow.

  • First of all, do-while loop code block gets executed.
  • do-while loop evaluates condition expression inside the parenthesis.
  • If condition expression evaluates to true, then do-while loop code block gets executed.
  • condition expression is evaluated again.
  • This execution process continues until the condition expression evaluates false.
  • Whenever condition expression evaluates to false, do-while loop terminates and control goes to the next statement after the do-while loop.

Here is the flowchart of do-while loop execution

Java Do While Loop Statement Flowchart Diagram

Java Do-While Loop Example Program

public class DoWhileLoop {
    public static void main(String[] args) {
        int count = 0;
        do {
        } while(count < 5);

In above program, do-while loop executes code block 5 times, till the time the value of count variable is less than 5. With each iteration the value of count variable is incremented. As soon as value of count becomes 5 do-while loop terminates.

Here are the execution steps for each iteration of do-while loop in above program.

Iteration Count Variable Do-While Code Block Condition(count < 5)
1 count = 0 Print count(0).
count is incremented to 1
2 count = 1 Print count(1).
count is incremented to 2
3 count = 2 Print count(2).
count is incremented to 3
4 count = 3 Print count(3).
count is incremented to 4
5 count = 4 Print count(4).
count is incremented to 5

Best Practices of Using Array Data Structures

  • Ensure an Exit Condition : Always ensure that there's a clear exit condition to prevent infinite loops. A do-while loop guarantees at least one execution, but it can still become infinite if the exit condition is never met.

  • Initialize Variables Outside the Loop : Initialize loop control variables outside the do-while loop to avoid unintentional reinitialization inside the loop.

  • Increment or Decrement Inside the Loop : Increment or decrement loop control variables inside the loop to avoid unintentional infinite loops or skipped iterations.

  • Use break Sparingly : While the break statement can be useful for exiting a loop prematurely, excessive use can make the code harder to understand. Consider refactoring the loop or using additional conditional statements to improve clarity.

  • Be Mindful of Initialization : Ensure that any variables used in the loop condition are properly initialized before the loop. Failure to initialize variables may result in compilation errors.

  • Keep Loop Body Simple : Keep the body of the do-while loop simple and avoid complex logic. If the loop body becomes too complex, consider refactoring the code into separate methods.

Advanced Do-While Loop Techniques

  • Nested Do-While Loops : Just like while loops, do-while loops can also be nested to handle more complex scenarios.
    public class NestedDoWhileLoopExample {
        public static void main(String[] args) {
            int outer = 1;
            do {
                int inner = 1;
                do {
                    System.out.println("Outer: " + outer + ", Inner: " + inner);
                } while (inner <= 3);
            } while (outer <= 3);
    In this example, the outer do-while loop executes three times, and for each iteration of the outer loop, the inner do-while loop executes three times, producing a total of nine output lines.

  • Do-While Loop for String Manipulation : do-while loops can be employed for string manipulation tasks, such as reversing a string.
    public class ReverseStringDoWhileExample {
        public static void main(String[] args) {
            String original = "Hello, World!";
            String reversed = "";
            int index = original.length() - 1;
            do {
                reversed += original.charAt(index);
            } while (index >= 0);
            System.out.println("Original: " + original);
            System.out.println("Reversed: " + reversed);
    In this example, the do-while loop iterates through the characters of the original string in reverse order, creating a reversed string.

  • Infinite Do-While Loop with a Break : You can create an infinite do-while loop and use a break statement to exit the loop based on a certain condition.
    public class InfiniteDoWhileLoopExample {
        public static void main(String[] args) {
            int count = 1;
            do {
                // Code
                if (count > 5) {
            } while (true);
    In this example, the do-while loop is intentionally infinite, and the break statement is used to exit the loop when the count exceeds 5.


The do-while loop in Java is a valuable tool for scenarios where you want to guarantee the execution of a block of code at least once. By mastering the basic syntax, understanding use cases, adopting best practices, and exploring advanced techniques, you can use the do-while loop effectively in your Java programs.

As you continue to develop your Java programming skills, practice using do-while loops in various scenarios. Whether you're building interactive menu-driven programs, validating user input, or processing collections, the do-while loop provides a robust and flexible solution. Consistent practice and adherence to best practices will enhance your ability to write clean, efficient, and maintainable code using do-while loops in Java.