корекция на код

else {
    for (int positionList1 = 0; positionList1 < firstList.size(); positionList1++) {
        newList.add(positionList1 * 2, firstList.get(positionList1));
    }
    int currentPositions = 1;

    for (int positionList2 = 0; positionList2 < secondList.size(); positionList2++) {
        newList.add(currentPositions, secondList.get(positionList2));
        currentPositions += 2;
    }
}