public void RemoveFirst()
{
if (Count != 0)
{
_head = _head.Next; // 2nd item becomes new head.
Count--; // Count decreases.
if (Count == 0)
{
_tail = null; // If there are no items, tail is now null too.
}
else
{
_head.Previous = null; // new head's Previous should point to null
}
// I wondered why this was in the if/else rather than simply being above Count--
// but I think it's because this operation is not necessary if the item had been
// a singleton and spares us one command in that case.
}
}
public void RemoveLast()
{
if (Count != 0)
{
_tail = _tail.Previous;
Count--;
if (Count == 0)
{
_head = null;
}
else
{
_tail.Next = null;
}
// I don't know why, but the book broke pattern here and created a
// if (Count == 1) case where _head and _tail are set to null.
// but this is accounted for with the above code, keeping the same pattern
// as our RemoveFirst method. I.e., if there is one item in the list,
// _tail.Previous is null so _tail becomes null. When you do Count--
// Count becomes 0, then _head is set to null, resulting in null/null.
}
}
public void Clear()
{
_head = null;
_tail = null;
Count = 0;
}