What is the difference between the methods areContentsTheSame and areItemsTheSame in the DiffUtil class and why are they needed?

In the DiffUtil class from Android, there are two key methods for comparing list items:

• areItemsTheSame — checks whether two objects represent the same item (for example, having the same unique identifier). This method answers the question: "Is this the same object in the list?".

• areContentsTheSame — checks whether the contents of two objects are the same, i.e., whether their data is equal. If the objects are considered the same item (areItemsTheSame returned true), this method determines whether the data of that item has changed.

Why is this needed: DiffUtil uses these methods to efficiently update the RecyclerView, minimizing the number of redraws. If areItemsTheSame returns false, the element is considered new. If true, but areContentsTheSame returns false, it means the element has changed and needs to be updated.

Example:

override fun areItemsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean {
    return oldList[oldItemPosition].id == newList[newItemPosition].id
}

override fun areContentsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean {
    return oldList[oldItemPosition] == newList[newItemPosition]
}