In this section, we will learn what the do-while loop is and how to use it in Java.

Note: we’re assuming you already familiar with the while loop.

What is do-while loop in Java?

The `do while` loop is another variant of the `while` loop and its difference is that it will run the body of the loop first and then check the condition of that loop. In such case, even if the output of the condition set for the loop is false, we’re guaranteed that at least the body will run for once.

Java do-while loop syntax

Here’s the structure of the `do while` loop:

do {
  // code block to be executed
}
while (condition);

`do` keyword: we use the keyword `do` and the pair of braces `{}` that come afterwards to define the body of the loop.

Again, this body is guaranteed to run at least once before checking the condition of the loop.

`while` keyword: we use the `while` keyword and the parentheses that come afterwards to set the condition of the loop.

Notes:

• As long as the condition is true, the body of the loop will run.
• Also the `while()` statement is set after the closing brace `}` of the `do` keyword.
• We use the semicolon `;` after the `while()` statement. 

Example: using do-while loop in Java

public class Simple {
    public static void main(String[] args) {
        int i = 0;
        do{
            System.out.print(i+", ");
            i++;
        }while (i != 100);
    }
}

Output: 
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99,

How does do-while loop work Java?

In this example, first the body of the loop ran and so the value of the `i` variable is sent to the output stream and also it is incremented by one before the condition of the while loop is checked. After that, the condition is checked to see if the value of this variable is equal to 100 or not and because this value is far away from 100, then the result of the condition is true and the body will run again.

This process will repeat itself until the value of the `i` variable becomes 100 which in that case the loop will break and the instructions after the loop will be executed.

Java Infinite do-while Loop

If we put a condition for a `do-while` loop that always returned true, then the body of that loop will never stop! This is a condition that is known as infinite while loop.

We seldom need to create an infinite loop in a program, but if ever you needed to create such loop, the simplest method to do so is to use the value `true` as the condition of a while loop.

That way, the condition will be true for as long as the program is running.

Example: Infinite do-while loop in Java

class Main{
	public static void main(String[] args) {
		System.out.println("Before the call to the do-while loop");
		do{
			// the body of the loop...
		}while(true)
		System.out.println("After the call to the do-while loop.");
	}
}

Note: because this loop is infinite, the statement after the do-while loop will never appear on the output.

Difference between do while and while in Java (Java do while vs while loop)

The biggest difference between a while loop and a do-while loop is on the order of checking condition of the loop and running the body of the loop!

For the `while` loop, it first starts with the condition and if the condition was true then the body of the loop will be executed! This means there’s chance that the body of the loop might never run (if the condition becomes false in the first place).

On the other hand, when it comes to the `do-while` loop, first the body of the loop will be executed and then the condition of the loop is checked. So this means at least one time the loop will be executed.