Question

which of these method implementations would correctly insert an element into an arraylist before every even index?

Answer 1

To correctly insert an element into an ArrayList before every even index, use the add(int index, E element) method of ArrayList in a loop that increments the index by 2 after each insertion, starting at index 0.

Step-by-step explanation:

The question is asking how to correctly insert an element into an ArrayList at positions before every even index. In Java, one can utilize the add(int index, E element) method of the ArrayList class to insert elements at specific indices. To insert an element before each even index, you would start from the beginning of the ArrayList and insert the new element at every second position, which requires incrementing the index by 2 after each insertion. If the ArrayList starts at index 0, then you would insert starting at index 0, then at index 2 (after insertion, this will be the new index 2 since the array is now larger), and so on. Here is an illustrative example:

ArrayList arrayList = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5));
for(int i = 0; i < arrayList.size(); i += 2) {
arrayList.add(i, newValue);
}

Note that every insertion will shift subsequent elements to the right, changing their indices, which is why it is crucial to increment 'i' by 2 because the ArrayList's size increases after each insertion.