In ArrayList methods, what is the primary difference between add() and set()?

• A. add() removes an element, set() adds an element
• B. add() shifts elements, set() replaces an element
• C. Both methods achieve the same outcome
• D. set() adds an element, add() does not

Answer: (B)

The primary difference between the add() method and the set() method in ArrayList relates to their specific functionalities within the list structure. The add() method is used to insert a new element into the list. When you use add(), if you don't specify an index, it appends the element to the end of the list. If you do specify an index, it will insert the element at that position and shift any elements that are currently at or after that index one position to the right to accommodate the new element.

On the other hand, the set() method is used to replace an existing element at a specified index in the list. When you call set(), it requires an index and will replace the current element at that index with the new element provided. It does not change the size of the list; it simply updates the value at that particular index.

Thus, the correct choice highlights that add() can shift elements when inserting new elements, while set() replaces the existing element without altering the overall size of the list.