merge two arraylist lists in list1 while it remain sorted

Question

In my assignment the third step is to Call the method merge to merge the two lists in list1 so that the list1 remains sorted.

I write my code but it

Answer 1

If your input Lists aren't too long, I'd suggest just merging the lists and using the Collections.sort() Method to restore the order:

public static void mergeAndSort(List list1, List list2) {
    List combinedList = new ArrayList(list1);
    combinedList.addAll(list2);
    Collections.sort(combinedList);
    return combinedList;
}

As a sidenote, you should use the List interface instead of the ArrayList implementation class wherever possible.