Recursively sorting an unbounded stack (java) in ascending order? (This assignment is only limited to stacks…

Recursively sorting an unbounded stack (java) in ascending
order? (This assignment is only limited to stacks only, No other
data structures are allowed)
My professor gave us a hint on how to implement this, however
she wants the comparable interface to be used. im not sure on how
to do this.
Hint: May want to use a public method that accepts the original
stack and then creates the two additional stacks needed. This
method then calls a private method that accepts all three stacks
and does the recursive sort. Your methods should make sure all
types of stacks passed contain comparable objects. Refer to the
generic presentation in Shared Files.
What I have : unboundedarray.java
import java.util.ArrayList;

public class UnboundedStack

{

   protected ArrayList element;
   public UnboundedStack()

   {

     element = new ArrayList();

   }
   public T peek() throws
StackUnderflowException

   {

     T topofstack = ;

     if(isEmpty())

     {

         throw new
StackUnderflowException(“Empty Stack”);

     }

     else

         topofstack =
element.get(element.size() – 1);

     return topofstack;

   }
   public void pop() throws
StackUnderflowException

   {

     if(isEmpty())

     {

       throw new
StackUnderflowException(“empty stack”);

     }

     else

        
element.remove(element.size() – 1);

   }
   public void push(T elements) throws
StackOverFlowException

   {

      element.add(elements);

   }
   public boolean isEmpty()

   {

      return (element.size() == 0);

   }
   public boolean isFull()

   {

     return false;

   }

}
my main class :
public class Recursivestack {
  

    public static UnboundedStack
initializeSort(UnboundedStack s)

    {

        UnboundedStack temp =
new UnboundedStack<();         UnboundedStack sort = new UnboundedStack<();         return temp; // this will need to be fixed     }                 public static void main(String args[])    {        UnboundedStack unsorted = new UnboundedStack<();        unsorted.push("kevin");        unsorted.push("brian");        unsorted.push("devon");        unsorted.push("larry");        unsorted.push("kaiden");        initializeSort(unsorted);    } }