Array FIFO - First In First Out without manually shifting array contents

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abefroman

Array FIFO - First In First Out without manually shifting array contents

in Programming Questions • 2 years ago

Hi everyone. I've searched the forums and haven't been able to find anything related to what I'm trying to do. I've been able to do it manually but I'm hoping for a more elegant solution.

I have a String array that's 10 elements long that I want to store incoming serial data in. But I want the newest data to be element [0], and the second newest to be [1] and so on - until the oldest incoming data gets "pushed off" the end of the array and deleted. So everything gets pushed down one element whenever new data comes in. I believe this is called FIFO (First In First Out).

I can easily accomplish this like so: (shortened to 3 elements)
lastThreeStrings[2] = lastThreeStrings[1];
lastThreeStrings[1] = lastThreeStrings[0];
lastThreeStrings[0] = incomingSerialString;

A while back I tried putting this into a loop and it didn't work, so I reverted to the above method but with 10 strings.

So the question is this: is there a more elegant way to do what I'm trying to do?

I thought of something like this:
lastThreeStrings = reverse(lastThreeStrings);
lastThreeStrings = shorten(lastThreeStrings);
lastThreeStrings = reverse(lastThreeStrings);
lastThreeStrings = expand(lastThreeStrings, 1);

But that seems a bit convoluted too, although it might seem less convoluted if I had an array with thousands of elements.

Any ideas? Thanks in advance.

Replies(9)

kooogy

Re: Array FIFO - First In First Out without manually shifting array contents

2 years ago

http://download.oracle.com/javase/1,5.0/docs/api/java/util/LinkedList.html implements Queue (java 1.5 and above). allows adding and removing at head or tail. nothing i can see restricts the size, but you can manage that yourself (checking size and deleting trailing items whenever things are added)

failing that, my old favourite, use an ArrayList as a circular buffer. http://www.java2s.com/Tutorial/Java/0140__Collections/CircularBuffer.htm

fiveagon

Re: Array FIFO - First In First Out without manually shifting array contents

2 years ago

I think you want java.util.Stack. Last In, First Out (LIFO)

Stack<String> stringStack = new Stack<String>();

This gets you all sorts of goodies.

stringStack.setSize(10); // Sets stack to 10 Objects, deleting oldest data.
for (String s : stringStack) { // Stack implements Iterable, so you can use in for-each loop
s.toUpperCase();
}
String newString = "This is the newest string we're putting in the stack";
stringStack.push(newString);
println(stringStack.get(0)); // prints the equivalent of newString
println(stringStack.peek()); // prints the equivalent of newString

kooogy

Re: Re: Array FIFO - First In First Out without manually shifting array contents

2 years ago

> I want the newest data to be element [0], and the second newest to be [1] and so on
> - until the oldest incoming data gets "pushed off" the end of the array and deleted."

nope, that's a queue

fiveagon

Re: Re: Array FIFO - First In First Out without manually shifting array contents

2 years ago

LOL, I'd hate to be in a "queue" in your place of business, kooogy. As long as new people got in line, I'd never get helped!

PhiLho

Re: Re: Array FIFO - First In First Out without manually shifting array contents

2 years ago

Why, fiveagon? That's the oldest, ie. the first to come in the line, that is "pushed off", ie. helped first.

fiveagon

Re: Re: Array FIFO - First In First Out without manually shifting array contents

2 years ago

I'm still not seeing how I'm wrong on this.

The OP wants 2 things:

He wants the newest and last data in to be at index 0. Last In, First Out.
He wants the oldest data to be pushed off, deleted, gone, bye bye. This part has nothing to do with "being helped".

amnon.owed

Re: Array FIFO - First In First Out without manually shifting array contents

2 years ago

A while back I tried putting this into a loop and it didn't work [...]

Why not? Ain't nothing wrong with a simple for loop...

int numStrings = 3;
String[] myStrings = new String[numStrings];
int count;
void setup() { }
void draw() { }
void keyPressed() {
if (key == ' ') {
addString("someString-" + nf(count++, 2));
println("==="); println(myStrings);
}
}
void addString(String newString) {
for (int i=numStrings-1; i>0; i--) {
myStrings[i] = myStrings[i-1];
}
myStrings[0] = newString;
}

abefroman

Re: Array FIFO - First In First Out without manually shifting array contents

2 years ago

Wow, thanks for the multiple quick responses!

kooogy, it looks like you've answered this type of question before. You simple mention of circular buffer was especially useful. I find Java Docs make my eyes glaze over, so you've at least steered me in a better direction.

And fiveagon, thanks too. I haven't tried Stack yet, but peek, get, and more Java Docs make me realize I'm still quite a newbie in all things programming!

amnon.owned, thanks for posting actual working code

. It was quite a while ago that I tried to put this in a loop and was probably just too new to get it right. But thanks for giving me a real working example of a successful way to do this via a loop. Since my project is more of a "get it done quick" type I'll probably use this simpler method and leave the proper learning for next time. But it's nice to know this post will be useful to me and others for a long while after this.

Thanks!

fiveagon

Re: Array FIFO - First In First Out without manually shifting array contents

2 years ago

Aggh. I misunderstood how Stack works. It doesn't automatically reindex everything. And using setSize() seems to break everything?

My bad guys.

Stack<String> stringStack = new Stack<String>();
int maxStackSize = 10;
int count;

void setup() {
}
void draw() {
}

void keyPressed() {
    if (key == ' ') {
        addString("someString-" + nf(count++, 2));
        println("===");
        for (String s : stringStack) {
            println(s);
        }
        println("---");
        println(stringStack.get(0));
        println(stringStack.peek());
    }
}

void addString(String newString) {
    stringStack.push(newString);
//    stringStack.setSize(maxStackSize);
}

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