class StackList implements StackInterface $\{$

$//$ Note: Stack follows the LIFO $("$Last In First Out"$)$ principle.

private Node top;

private int size;

$//$ add item on top

$//$ O$(1)$

public void push$($T item$)\{$

$//$ save the prev. top$/$node in a temp variable

Node prev $=$ top;

$//$ init. top to a new node and pass in the item and prev. node

top $=$ new Node$($item$,$ prev$)$;

$//$ increment size

size$++$;

$\}$

$//$ remove item on top and returns it back to the user$/$caller

$//$ O$(1)$

public T pop$()\{$

if$($top $==$ null$)\{//$ OR size $==0$

System.out.println$("$unable to pop, stack is empty"$)$;

return null;

$\}$

$//$ save the item that will be returned back to the caller

T itemOnTop $=$ top.getItem$()$;

$//$ remove the item on top

top $=$ top.getNext$()$;

$//$ decrement size

size$--$;

$//$ return item that was on top

return itemOnTop;

$\}$

$//$ without popping, return item on top of the stack

$//$ O$(1)$

public T peek$()\{$ return null; $\}$

$//$ O$(1)$

public boolean isEmpty$()\{$ return false; $\}$

$//$ O$(1)$

public int size$()\{$ return $0$; $\}$

$//$ O$($N$)$

public boolean contains$($T item$)\{$ return false; $\}$

$\}$Convert StackList from "Week $-05"$ to use Arrays instead of Nodes, call it: StackArray.java

Unlike Nodes, arrays have a hard capacity which needs to be taken into account when implementing this data structure

A Stack follows the LIFO $($Last In First Out$)$ principle, which means items are added $($pushed$)$ at the "top" of the data structure and removed $($popped$)$ from the "top"

In an array, "top" would the the last item in the array that is not null

HINT: One can use an integer variable to keep track $($bookkeeping$)$ of the index that is considered the "top" most item in the Stack array