[Tutor] confused by linked queue

[Danny Yoo]

>> This works on a different principle than the linked list queue, but it 
>> does the same stuff.  The main idea is that a "queue" can be anything, 
>> as long as it supports three operations:
>>
>>      * isEmpty
>>      * insert
>>      * remove
>>
> <<snip>>
>
> Isn't there a fourth operation needed?
>
> 	* isFull

Hi Barry,

If we add this requirement, then we're talking about a queue with bounds. 
That is a perfectly reasonable thing to ask for, and it may or may not be 
an essential property in applications that use queues, depending on our 
application.  Small interfaces are easier to implement than large ones, so 
we should be try to put as few operations as necessary.


In any case, I think we're straying from the main point, which is the idea 
that we can implement a concept in many different ways.

The really simple ArrayQueue class presented earlier should "work" just 
like the LinkedQueue class.  So in practical terms, if we needed a queue 
for some application, we can use the simple thing first.  And if it turns 
out that the Queue implementation we've used is too slow, we can switch. 
No one should know the difference.

(I wouldn't immediately use LinkedQueue only because I don't trust it.  I 
mean that from an engineering point of view: the code has a heck of a lot 
of moving parts, and because I don't see a test suite for it, I can't be 
sure that it's correct without spending time on it.  Queues are boring; I 
don't want to spend time on them unless I really need to.  *grin*)


Good programmming practice allows us to be non-committal in the places 
where we want to support change.