How can I instantiate an array of Stacks of type i

Question

I am trying to create an array of stacks, in which each stack within the array is of type int.

If I create the array like this:  Stack<Integer>[] numbers = new Stack<Integer>[3]; , there is the compile error  "Cannot create a generic array of Stack<Integer>". So, I am trying to create the array of Stacks with the wildcard type instead of Integer,  and it then does not have this error.

However, if I then try to push an int into one of the stacks (of wildcard "?" type) like this:  this.numbers[stackIndex].push(i); , there is the compile error  "The method push(capture#1-of ?) in the type Stack<capture#1-of ?> is not applicable for the arguments (int)".

So, how can I properly instantiate an array of Stacks of type int? As of now I am not able to perform push/pop operations on these Stacks...

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My reasoning in this is an attempt to program the Tower of Hanoi game. I wanted each of the three rods to be a Stack of type int, each ring to be represented as an int, and the three rods together to be contained as an array of the three Stacks.

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Here is some example code:

import java.util.Stack;

public class StackTest {

    Stack<?>[] numbers;

    public StackTest(int stackLength) {
        this.numbers = new Stack<?>[stackLength];
    }

    public void fillStack(int stackIndex, int numRings) {
        for (int i = numRings; i >= 0; i--) {

            // this statement has a compile error!
            this.numbers[stackIndex].push(i);
        }
    }

    public static void main(String[] args) {
        int numberOfRods = 3;
        StackTest obj = new StackTest(numberOfRods);

        int rodNumber = 0, numberOfRings = 4;
        obj.fillStack(rodNumber, numberOfRings);
    }
} // end of StackTest

Answer 1

My guess is that you should push an Integer rather than an int:

this.numbers[stackIndex].push(Integer.valueOf(i));

Answer 2

One solution could be:

public class StackInteger extends Stack<Integer> {
}

And then:

StackInteger[] numbers = new StackInteger[3];

Or even:

Stack<Integer>[] numbers = new StackInteger[3];

Answer 3

It has to be a raw Stack[] or you can use List<Stack<YourClass>> lstStack = new ArrayList<Stack<YourClass>>().

In this case, I would prefer to use

List<Stack<Integer>> lstStack = new ArrayList<Stack<Integer>>(stackLength);