public int[] front11(int[] a, int[] b) {
  if (a.length == 0 && b.length == 0) return new int[0];
  if (a.length == 0) return new int[] {b[0]};
  if (b.length == 0) return new int[] {a[0]};
  return new int[] {a[0], b[0]};
}

Create front11.java