Find missing numbers in a range, when a sorted array with two elements with range repeat once

Suggestions for cleanup and optimization request.

This question is a follow-up question on this post.

Lets assume the range of 1, 2, 3, 4.

This function takes in an array of repeated elements, [1,1,4,4] and the output is [2, 3].

The question marked as duplicate takes an input of [1, 4] and output is [2, 3].

While output is same, the input differs.

Please make a note of this difference between two questions causing confusion.

final class Variables {
    private final int x;
    private final int y;

    Variables(int x2, int y2) {
        this.x = x2;
        this.y = y2;
    }

    public int getX() {
        return x;
    }

    public int getY() {
        return y;
    }

    @Override public String toString()  { 
        return "x = " + x + " y = " + y;
    }
}


    public final class FindMissingRepeating {

        /**
         * Takes an input a sorted array with only two variables that repeat once. in the
         * range. and returns two variables that are  missing.
         * 
         * If any of the above condition does not hold true at input the results are unpredictable.
         * 
         * Example of input:
         * range: 1, 2, 3, 4
         * input array [1, 1, 4, 4]
         * the variables should contain 2 missing elements ie 2 and 3
         * 
         * @param a : the sorted array.
         */
        public static Variables sortedConsecutiveTwoRepeating (int[] a, int startOfRange) {
            if (a == null) throw new NullPointerException("a1 cannot be null. ");

            int low = startOfRange;
            int high = low + (a.length - 1);

            int x = 0;
            int i = 0;
            boolean foundX = false;

            while  (i < a.length) {
                if (a[i] < low) {
                    i++;
                } else {
                    if (a[i] > low) {
                        if (foundX) {
                            return new Variables(x, low);
                        } else {
                            x = low;
                            foundX = true;
                        }
                    }
                    low++;
                    i++;
                } 
            }

            int val = foundX ? x : high - 1;
            return new Variables(val, high);
         }



        public static void main(String[] args) {
            int[] ar1 = {1, 2, 2, 3, 4, 4, 5};
            Variables v1 = FindMissingRepeating.sortedConsecutiveTwoRepeating (ar1, 1);
            System.out.println("Expected x = 6, y = 7 " + v1);

            int[] ar2 = {2, 2, 4, 4, 5, 6, 7};
            Variables v2 = FindMissingRepeating.sortedConsecutiveTwoRepeating (ar2, 1);
            System.out.println("Expected x = 1, y = 3 " + v2);

            int[] ar3 = {3, 3, 4, 4, 5, 6, 7};
            Variables v3 = FindMissingRepeating.sortedConsecutiveTwoRepeating (ar3, 1);
            System.out.println("Expected x = 1, y = 2 " + v3);

            int[] ar4 = {1, 3, 3, 4, 4, 6, 7};
            Variables v4 = FindMissingRepeating.sortedConsecutiveTwoRepeating (ar4, 1);
            System.out.println("Expected x = 2, y = 5 " + v4);
        }
    }