What is the difference between the areItemsTheSame and areContentsTheSame methods in the DiffUtil class when comparing items?

In the DiffUtil class, which is used for efficient list updates in Android (for example, in RecyclerView), there are two key methods for comparing items:

• areItemsTheSame — checks whether two objects represent the same item. Usually, unique identifiers (IDs) are compared. If the method returns true, it means it is the same item in the list, even if the content might have changed.

• areContentsTheSame — checks whether the contents of two items are the same, i.e., whether the data displayed to the user has changed. If it returns false, it means the item has changed and needs to be updated in the UI.

Example:

override fun areItemsTheSame(oldItem: Item, newItem: Item): Boolean {
    return oldItem.id == newItem.id
}

override fun areContentsTheSame(oldItem: Item, newItem: Item): Boolean {
    return oldItem == newItem // compare all fields
}

Thus, areItemsTheSame is responsible for item identity, and areContentsTheSame for their content and the need for updating.