Program-To find missing number in array 

1. class MissingNumber
2. {
3. public static void main(String args[])
4. {
5. int []arr={1,2,3,5,6,7};
7. System.out.println("missing number from this array is :"+missingElement(arr));
8. }
9. public static int missingElement(int arr[])
10. {
11.     int n=arr.length+1;
12. int es=n*(n+1)/2;
13. int ac=0;
14. for(int i=0;i< arr.length;i++)
15. {
16. ac=ac+arr[i];
17. }
18. return es-ac;
19. }
20. }