Java While Loop: Syntax, Execution Flow and Practical Programs

The while loop is an entry-controlled loop that repeatedly executes a block of target statements as long as its boolean condition remains true. The condition is verified at the entry gate before each iteration.

Syntax and Operational Flow

// While Loop Syntax:
while (boolean_condition) {
    // Loop body statements
    // Update statement (increments, decrements, or state change)
}

Practical Example: Reversing an Integer

A classic university exam program demonstrating a while loop where the iteration count depends on the numerical value:

public class ReverseNumberDemo {
    public static void main(String[] args) {
        int number = 12345;
        int reversed = 0;

        System.out.println("Original Number: " + number);

        while (number != 0) {
            int lastDigit = number % 10;       // Extract last digit
            reversed = reversed * 10 + lastDigit; // Append to reversed
            number = number / 10;              // Discard last digit
        }

        System.out.println("Reversed Number: " + reversed); // 54321
    }
}

Dry-Run Execution Trace Table