Find an element in an infinite length sorted array

Question

Given an infinite length sorted array having both positive and negative integers. Find an element in it.

EDIT
All the elements in the array are

Answer 1

--Complete Solution-- takes O(logn) time complexity

public class B {

public static void main(String[] args) {
    // Assuming sorted array of infinite length
    int a[] = new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 };

    int elementToFind = 12;

    int finalIndex = getFinalIndex(a, elementToFind);

    if (finalIndex == -1) {
        System.out.println("Element not found");
    }
    System.out.println("Found element:" + a[finalIndex]);

}

private static int getFinalIndex(int[] a, int elementToFind) {

    int power = 2;
    int finalIndex = (int) Math.pow(2, power);

    for (int i = 0; i < finalIndex;) {

        if (elementToFind == a[finalIndex]) {
            return finalIndex;
        }

        else if (elementToFind < a[finalIndex]) {
            System.out.println("search through binary search algo");
            // taking i as starting index in binary search call
            int searchedIndex = callToBinarySearch(a, i, finalIndex);
            return searchedIndex;
        }

        else {
            i = finalIndex + 1;
            power = power * 2;
            finalIndex = (int) Math.pow(2, power);

        }
    }
    return -1;

}

}