Java Do-while Loop

Do-while Loop

Java Do-while Loop is used to execute a code block repeatedly in a loop based on a condition, with the exception that the code block is executed at least once.

In this tutorial, we will learn the syntax of do-while loop statement and demonstrate some of the scenarios of do-while loop using example programs.

Syntax

The syntax of do-while loop is

do {
     statement(s)
 } while(condition);

where do and while are Java keywords, statement(s) is a set of valid Java statements, and condition is an expression which must evaluate to a boolean value.

The statement(s) inside the block are executed, and the condition is evaluated. As long as the condition is true, the statement(s) inside the block are executed in a loop; or else if the condition is false, the execution of do-while is completed.

Examples

Simple Do-while Loop

In the following program, we write a do-while loop to print messages in a loop.

Example.java

public class Example {
	public static void main(String[] args) {
		int i = 0;
		do {
			System.out.println("hello world " + i);
			i++;
		} while(i < 4);
	}
}

Output

hello world 0
hello world 1
hello world 2
hello world 3

Do-while Loop with Break Statement

We can break a do-while loop using break statement. This breaks the loop even before the condition evaluates to false.

Example.java

public class Example {
	public static void main(String[] args) {
		int i = 0;
		do {
			if (i == 3) {
				break;
			}
			System.out.println("hello world " + i);
			i++;
		} while(i < 8);
	}
}

Output

hello world 0
hello world 1
hello world 2

Do-while Loop with Continue Statement

You can skip the execution of code block by using continue statement.

Example.java

public class Example {
	public static void main(String[] args) {
		int i = 0;
		do {
			if (i == 3) {
				i++;
				continue;
			}
			System.out.println("hello world " + i);
			i++;
		} while(i < 8);
	}
}

Output

hello world 0
hello world 1
hello world 2
hello world 4
hello world 5
hello world 6
hello world 7

Find Factorial using Do-while Loop

In the following java program, we shall find the factorial of a number using do-while loop.

Example.java

public class Example {
	public static void main(String[] args) {
		int n=6;
		
		//initialization
		int factorial = 1;
		int i = 1;
		
		do {
			factorial = factorial*i;
			i++;
		} while(i <= n);
		
		System.out.println("Factorial of " + n + " : " + factorial);
	}
}

Output

Factorial of 6 : 720

Conclusion

In this Java Tutorial, we learned how to write a do-while loop in Java and covered some of the use cases that use do-while loop.