Java While Loop: Syntax, Flowchart, and Examples

Java While Loop

A Java While Loop is a control flow statement that allows code to be executed repeatedly until a certain condition is met. It is often used when the number of iterations isn't fixed, and the loop continues until the condition is no longer true. The while loop syntax in Java is as follows:

while (condition) {
    // statements
}

In a while loop, the condition is evaluated first. If the condition is true, the code within the loop is executed. The condition is then checked again, and this process continues until the condition is no longer true, at which point the loop terminates.

While Loop Flowchart

1. Control falls into the while loop.
2. The flow jumps to the condition.
3. The condition is tested.
4. If the condition yields true, the flow goes into the body of the loop.
5. The statements inside the loop are executed.
6. The condition is updated.
7. Control flows back to step 2.
8. The while loop has ended, and the flow has gone outside.

Examples of While Loop

Simple While Loop

In this example, a while loop is used to print the integer numbers in reverse order starting from 10.

public class WhileLoopExample {
    public static void main(String args[]) {
        int i = 10;
        while (i > 1) {
            System.out.println(i);
            i--;
        }
    }
}

Output: 10 9 8 7 6 5 4 3 2 1

Infinite While Loop

An infinite while loop is a loop that never ends. In this example, the condition is never met, causing the loop to execute indefinitely.

public class InfiniteWhileLoopExample {
    public static void main(String args[]) {
        while (true) {
            System.out.println("Infinite loop");
        }
    }
}

This program will keep printing "Infinite loop" until it is manually stopped.

Breaking a While Loop

There are several ways to break a while loop in Java:

• Using a break statement: This allows you to exit the loop prematurely.
• Altering the Boolean condition: If the condition becomes false, the loop will terminate.
• Using a return statement: This causes the program to exit the function, and any while loops within the function will also terminate.
• Using the System.exit() method: This terminates the Java Virtual Machine, stopping all loops and programs.

Exercises

To practice working with while loops, try the following exercises:

• Use a while loop to print the numbers 1 to 10, then 10 to 1.
• Write a program that calculates the sum of numbers entered by the user until they enter a negative number.
• Create a program that counts the number of times a user enters a vowel in a sentence.