Java Queue

[aKobrakai]

For a lab, our class had to write a queue in java. Mine works fine, but my professor doesn't like how it "resets" when it is empty. He wants me to do it over, but I have no idea how else to write it. Anyone have a solution that doesnt set front and rear to 0 when it is empty?

[faulkner132]

Were you supposed to use an array? Using a static type doesn't really make since to me when trying to model something dynamic like a queue.

Maybe he wanted you to use a linked list or a vector instead. This way you wouldn't have to use variables to keep track of locations... the structures would do that for you. Resetting would be as simple as something like x = new [Structure].

[aKobrakai]

We were forced to use an array of int. He wanted use to keep track of the top and bottom like I did. The only thing he really told us was that we shouldn't use one position in the array (I dont use the first position, but the way he showed us was a spot in the middle), and we should treat the array like a circle. He could be completely wrong, he is the worst professor I have had, and I highly doubt he has a working program the way he wants us to do it.

[faulkner132]

If he wants you to think about it like a circle, then the best analogy I can come up with is a revolver. The space remains the same, yet the "start" of the structure changes everytime a bullet is fired. The first would change each time, but the last would only change when you load another bullet. This way you wouldn't have to reset, because when first = last it is already in the reset position.

I think this is a really poor way to teach a first in - first out concept. I prefer the simple lunch line example, but oh well. Hope I was of some help.

[aKobrakai]

What I don't understand is how to deal with the fact that first=last when the queue is empty, and when it is full.

[faulkner132]

Good point, if there is no data in first, it is empty.

Think of the revolver again.
When it is fully loaded (6 bullets): first=1 and last=1
Fire: first=2 last=1
Fire: first=3 last=1
Fire: first=4 last=1
Fire: first=5 last=1
Fire: first=6 last=1
Fire: first=1 last=1 -- Empty (Condition is (first = last AND first has no data)

If you add data at any point during the dequeue process then simply increment last.

[aKobrakai]

Thanks for the response, but how do you check to see if there is no data on an array of int? I could be wrong, but I don't believe you can have null on an array of int.

[faulkner132]

He should have given you a value (0, -1, etc.) to indicated there is no value. This way when you go to remove data from the queue you can reset the value. If he didn't then I have no idea what you can do short of creating a boolean which flags whether or not there is data.