I need help writing a method in java, that prepends an existing array and then doubles the array when I run out of space. Like below except this array is not doubling. Also I cannot use a loop, for efficency. This is what I have so far:

[9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 0, 0, 0, 0] [8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 0, 0, 0] [7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 0, 0] [6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 0]

public void prepend(int x) { if (length >= a.length){ int[]b = new int[a.length + 1];

for (int i = 0; i < a.length; i++){ b1[i] = a[i]; } a = b; } length = length + 1; }