Do While Loop ​

In Java, the while loop first determines the loop condition and then executes the loop. Another type of do while loop executes the loop first and then judges the conditions. When the conditions are met, the loop continues and exits when the conditions are not met. Its usage is:

do {
//Execute loop statement
} while (condition);

It can be seen that do while loop will loop at least once.

Let’s rewrite the sum of 1 to 100 using do while loop:

// do-while
public class Main {
  public static void main(String[] args) {
    int sum = 0;
    int n = 1;
    do {
      sum = sum + n;
      n ++;
    } while (n <= 100);
    System.out.println(sum);
  }
}

When using do while loops, you must also pay attention to the judgment of loop conditions.

Practise ​

Use do while loop to calculate the sum from m to n .

// do while
public class Main {
	public static void main(String[] args) {
		int sum = 0;
        int m = 20;
		int n = 100;
		// Use do while to calculate M+...+N:
		do {
		} while (false);
		System.out.println(sum);
	}
}

Summary ​

do while first executes the loop and then determines the condition;

do while loop will be executed at least once.