Find Missing number in Java Puzzle

Find missing number in java puzzle

public class JavaPuzzle { int sumOfTotalNnumbers(int num) { int sum = (num * (num+1))/ 2; return sum; } int sumOfAllElements(int[] items) { int sum = 0; for (int i = 0; i < items.length; i++) { sum = sum + items[i]; } return sum; } public static void main(String[] args) { JavaPuzzle jp=new JavaPuzzle(); int num = 10; int[] items = {1, 2, 5, 3, 7, 8, 6,9,4}; int son = jp.sumOfTotalNnumbers(num); int soi = jp.sumOfAllElements(items); System.out.println(son-soi + " is the missing number"); } }