Use an ArrayList ;)

List<Integer> numberList = new ArrayList<Integer>();

When you click yes and add a number, have this:
numberList.add(value);
You won't need to cast the int as an Integer because Java automatically autoboxes (converts primitives to Objects).

When you click no, try this:
int total = 0;
for (int i : numberList) {
total += i;
}
int average = total / numberList.size();

Hopefully that helps Good luck

A good way to solve computer programs is to plan them out before you begin coding. This gives you the time and space to make mistakes and get it straight where you are going- like a route map so you dont get lost.

Your program needs to:
- accept values,
- store values (the numbers read in, the total so far, and a count of how many values have been read in so far)
- loop and process the values
- output the average

Here is some sample pseudocode that should give you an idea of what to do here

Begin Program
initialize inputPrompt = "no"
initialize total = 0
initialize count = 0
intialize average = 0.0

Output prompt Yes / No //these are your buttons

While buttonClick not equal to "No" //this is the loop

Output prompt "enter a number"
accept and store input number //this is your input
count = count + 1 //this is your processing
total = input + total
average = total / count
Output prompt Yes / No //the user is prompted with the buttons again

End While
output average //output
End Program

You would use an array if you know how many numbers the user will enter, if its just 2 then just have 2 variables (if you need to keep a record of what they were).

You would use an arraylist if you dont know how many numbers the user will enter because it will expand to accomodate them, although it will not store primitive values like int. I think this is just a procedural programming problem you have been set anyway.