Do-While Loop

In Java, a do-while loop is a control flow statement that allows a program to repeatedly execute a block of code at least once, and then continue executing as long as a specified condition is true. The do-while loop is similar to the while loop, but the condition is evaluated after the first iteration, ensuring that the code inside the loop is executed at least once.

The basic syntax of a do-while loop in Java is as follows:

                
    do {
      // code to execute at least once
    } while (condition);

In this example, the condition is a boolean expression that is evaluated at the end of each loop iteration. If the condition is true, the loop continues to execute. If the condition is false, the loop terminates.

Here's an example of how a do-while loop can be used in Java to prompt the user to enter a number, and then validate the input to ensure it is positive:

                
    import java.util.Scanner;

    public class DoWhileExample {
      public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int number;

        do {
          System.out.println("Enter a positive number: ");
          number = scanner.nextInt();
        } while (number <= 0);

        System.out.println("You entered " + number);
      }
    }

In this example, the program prompts the user to enter a positive number using the System.out.println() method. The program then reads the user's input using the Scanner.nextInt() method and assigns the value to the number variable. The loop continues to execute as long as number is less than or equal to 0. Once the user enters a positive number, the condition becomes false and the loop terminates. The program then prints the value of number to the console.

Do-while loops in Java can be used to perform a wide variety of tasks, such as validating user input, processing data in batches, or waiting for a particular condition to be met. Do-while loops are particularly useful when a block of code must be executed at least once before the condition is evaluated.

One thing to note is that do-while loops can also be prone to infinite loops if the condition never becomes false. To prevent this, it's important to ensure that the condition will eventually become false based on the inputs or logic of the program.

Overall, do-while loops provide a powerful way to iterate over code in Java when at least one iteration must be performed, regardless of the condition.

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