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max = dataItems[???].getValue();
replace ??? with
count
That's your variable in the for loop.

double min = dataItems[0].getValue(),
double max = dataItems[0].getValue(),
double sum = dataItems[0].getValue();

Have an array of Items that are the length of number of items entered by Scanner.

Item[] items = new Item[numOfDataItems];

Have a for loop for each item

for (int i =0; i < items.length; i++)...

Are you scanning from a file or from the console?

If from the console

do something like

Scanner console = new Scanner(System.in);

if from a file

It's better if you post all of your code, see how to in my signature.

also, it's kinda hard to help when we don't know what's going wrong.

What are you trying to do?