Do While Loop

Do while loop is aexit controlled loop. That is the condition is checked at the end of the loop thats why if condition does not satisfy , the loop statements are executed at least once.

Do while loop mostly used in the menu driven programs like to display the MENU to user again and again until exit button is pressed.

Do While Loop Syntax

do
{
   // body of do while loop
   // increment or decrement
   
} while(condition);

Flowchart

Syntax Explanation by comparing with while loop

• The while loop tests the condition before executing any of the statements within while loop.
• Do-while loop tests the condition after having executed the statements within the loop.
• Do-while loop would execute its statements atleast once,even if the condition fails for the first time.
• while loop will not execute it's statements if the condition failes for the first time.

Example

Following programs will clear the exact difference between while loop and do-while loop.

Using While loop

public class Test 
{
   public static void main(String[] args) 
   {
      String msg = "Androidberry";
		
      while(msg.equals("Java"))
      {
         System.out.println("Hello There");
      }
   }
}

Output

No output - Because while loop is not executed.

Using Do While loop

public class Test 
{
   public static void main(String[] args) 
   {
      String msg = "Androidberry";
      do
      {
         System.out.println("Hello There");
		    
      }while(msg.equals("Java"));
   }
}

Output

Do while loop Example

In real life programming, we don't know when the user will stop providing values to the computer. In that situation we can use do-while loop for executing certain period time.

import java.util.Scanner;
public class Test 
{

   public static void main(String[] args) 
   {
      int length,choice=0;
      String str;
      Scanner sc = new Scanner(System.in);
		
      do 
      {
	 System.out.println("Enter string : ");
	 str = sc.next();
	 length = str.length();
	 System.out.println("Length of String is : "+length);
			
	 System.out.println("Do want to try another string? (1 = Yes| 2= No) : ");			
	 choice = sc.nextInt();
      }while(choice !=2);
   }
}

Output