Setting by Index

set does the opposite of get. Instead of reading the value at an index, it overwrites that value. Here it is:

public void set(int index, T value) {
  if (index < 0 || index >= size) {
    throw new IndexOutOfBoundsException();
  }
  node(index).value = value;
}

Reaching the node takes $O(n)$. The assignment itself is $O(1)$. In DynamicArray, this was $O(1)$ because it could index directly into the array in constant time.

This is why node returns a Node<T> instead of a T value: to set the value, we need to reach the node and then overwrite its value field.