Add the following methods to the LinkedStack class, and create a test driver for each to show that they work correctly. In order to practice your array related coding skills, code each of the methods by accessing the internal variables of the LinkedStack, not by calling the previously defined public methods of the class.

a. String toString() - creates and returns a string that correctly represents the current stack. Such a method could prove useful for testing and debugging the each

class and for testing and debugging applications that use the class. Assume each stack element already provided its own reasonable toString method.

import support.LLNode;

public class LinkedStack implements StackInterface { protected LLNode top; // reference to the top of this stack

public LinkedStack() { top = null; }

public void push(T element) // Places element at the top of this stack. { LLNode newNode = new LLNode(element); newNode.setLink(top); top = newNode; }

public void pop() // Throws StackUnderflowException if this stack is empty, // otherwise removes top element from this stack. { if (isEmpty()) throw new StackUnderflowException("Pop attempted on an empty stack."); else top = top.getLink(); }

public T top() // Throws StackUnderflowException if this stack is empty, // otherwise returns top element of this stack. { if (isEmpty()) throw new StackUnderflowException("Top attempted on an empty stack."); else return top.getInfo(); }

public boolean isEmpty() // Returns true if this stack is empty, otherwise returns false. { return (top == null); }

public boolean isFull() // Returns false - a linked stack is never full { return false; }

}