Implement the following methods for an Arraylist in Java

public void add(int index, E element) {

// Add element at index.

}

public E remove(int index) {

// Remove the element at index. Make sure there are no gaps

// Return the removed element

}

public int indexOf(Object o) {

// Returns the index of the first occurrence of the specified element

// in this list, or -1 if this list does not contain the element.

}