Java do-while loop is used to execute a block of statements continuously until the given condition is true. The do-while loop in Java is similar to while loop except that the condition is checked after the statements are executed, so do while loop guarantees the loop execution at least once.
Java do while loop
Java do while loop syntax is as follows:
do {
// statements
} while (expression);
The expression for the do-while loop must return a boolean value, otherwise, it will throw compile-time error.
do while java flow diagram
Java do-while loop example
Here is a simple java do-while loop example to print numbers from 5 to 10.
package com.journaldev.javadowhileloop;
public class JavaDoWhileLoop {
public static void main(String[] args) {
int i = 5;
do {
System.out.println(i);
i++;
} while (i <= 10);
}
}
do while true java
We can create an infinite loop by passing boolean expression as true in the do while loop. Here is a simple do while java infinite loop example.
package com.journaldev.javadowhileloop;
public class DoWhileTrueJava {
public static void main(String[] args) throws InterruptedException {
do {
System.out.println("Start Processing inside do while loop");
// look for a file at specific directory
// if found, then process it, such as inserting rows into database
System.out.println("End Processing of do while loop");
Thread.sleep(5 * 1000);
} while (true);
}
}
Note that you will have to manually quit the application to stop it, using Ctrl+C if the program is executed in the terminal. If you execute the program in Eclipse IDE then there is a red color button to terminate the program.
do while vs while loop
The only time you should use a do-while loop is when you want to execute the statements inside the loop at least once, even though condition expression returns false. Otherwise, it’s always better to use a while loop. Java while loop looks cleaner than a do-while loop. That’s all for java do while loop. You should also look into java for loop and java continue statement. Reference: Oracle Documentation
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hi Pankaj, Can you please correct the “if condition is true arrow” in the image?
- Nikhil
Ah, thanks for noticing that small mistake. I have corrected the image now.
- Pankaj
Hey, can I ask for some help coz im having a trouble. I want to repeat and repeat converting in my program if I enter Yes and it will stop if I will enter No but im really having a trouble. I wish you could help me. Here is my code: import java.util.*; import java.text.DecimalFormat; class CurrencyConverter { public static void main(String args[]) { double amount, Dollar, Pound, Yen, Won, Euro, Baht, Yuan, Lira, Franc, Rupee; DecimalFormat f = new DecimalFormat(“#,###,###.###”); Scanner sc = new Scanner(System.in); String[] currencyList = new String[] {" Dollar", " Pound", " Yen", " Won", " Euro", " Baht", " Yuan", " Lira", " Franc", " Rupee"}; { System.out.println(“°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°”); System.out.println(“Hi!😃 Welcome to Currency Converter!”); System.out.println(“°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°”); System.out.println(“Which currency you want to convert your ₱eso? Please choose.👇”); for (int x = 0; x < currencyList.length; x++) { System.out.println(x + 1 + “.” + currencyList[x]); } boolean repeat = true; int num = 0; String answer; do{ System.out.println(“°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°”); System.out.print(“Currency no. “); int code = sc.nextInt(); System.out.println(“°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°”); System.out.println(“Please enter the how much you want to convert.”); System.out.print(“₱ “); amount = sc.nextInt(); repeat = true; if (code == 1) { Dollar = amount * 50.76; System.out.println(” Its " + f.format(Dollar) + " dollars.”); } else if (code == 2) { Pound = amount * 62.48; System.out.println(” Its " + f.format(Pound) + " pound.”); } else if (code == 3) { Yen = amount * 0.47; System.out.println(" Its " + f.format(Yen) + " yen.“); } else if (code == 4) { Won = amount * 0.041; System.out.println(“Its " + f.format(Won) + " won.”); } else if (code == 5) { Euro = amount * 54.87; System.out.println(“Its " + f.format(Euro) + " euro.”); } else if (code == 6) { Baht = amount * 1.57; System.out.println(” Its " + f.format(Baht) + " baht."); } else if (code == 7) { Yuan = amount * 7.16; System.out.println(“Its " + f.format(Yuan) + " yuan.”); } else if (code == 8) { Lira = amount * 7.27; System.out.println(“Its " + f.format(Lira) + " lira.”); } else if (code == 9) { Franc = amount * 52.18; System.out.println(“Its " + f.format(Franc) + " franc.”); } else if (code == 10) { Rupee = amount * 0.66; System.out.println(“Its " + f.format(Rupee) + " rupee.”); } else System.out.println(“❗I N V A L I D C O D E❗”); String invalid = sc.nextLine(); { System.out.println(“°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°”); System.out.println(“Do you want to convert again? Yes or No”); answer = sc.nextLine(); repeat = true; } } while (answer.equals(“Yes”)); } } }
- Marie
Hi Marie, What is the purpose of using String invalid = sc.nextLine(); in your code?
- Annamalai
please give syntax for do while loop
- rupesh
do { statements; } while(condition);
- dhanya attaluri
The image still displays the wrong arrow…
- Roman
Please provide more examples rather than 1 on each type
- Ariyan sinha
import java.util.*; public class accepting { public static void main(String[] args) { //accept System.out.println (“Programe to accept your name”); Scanner sc = new Scanner(System.in); System.out.print("Enter Fullname : "); String fullname = sc.nextLine(); System.out.print("Enter Lastname : "); String lastname = sc.nextLine(); System.out.print("Enter Nickname : "); String nickname = sc.nextLine(); System.out.print(“Enter Student ID : “); String id = sc.nextLine(); //output System.out.println (”\n” + fullname + " " + lastname + " " + nickname + " " + id); } }
- VARAPON YUSOP