Java do-while Loop Interview Scenario

Java - do-while Loop

Q1. How can input validation be implemented in Java using a do-while loop ?

Input validation in Java can be effectively implemented using a do-while loop when the program must execute a block of code at least once, regardless of the condition.

A do-while loop first executes the loop body and then checks the condition. This makes it ideal for scenarios where user input is required before validation.

Example: Validating Positive Number Input

import java.util.Scanner;

public class PositiveNumberInput {

    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

The loop executes at least once to prompt the user for input.

If the user enters a value less than or equal to zero, the condition remains true and the loop repeats.

The loop terminates only when a valid positive number is entered.

This guarantees valid input before the program continues.

Why do-while is the Best Choice

Ensures at least one execution of the loop

Condition is evaluated after user input

Ideal for menu-driven programs and input validation

Improves user experience by preventing premature termination