Complete the implementation of the ArrayStack class presented in this chapter, specifically, complete the implementation of the isEmpty, size, and toString methods.

/* * To change this license header, choose License Headers in Project Properties. * To change this template file, choose Tools | Templates * and open the template in the editor. */ package jsjf;

import jsjf.exceptions.*; import java.util.Arrays;

/** * An array implementation of a stack in which the bottom of the * stack is fixed at index 0. * * @author Lewis and Chase * @version 4.0 */ public class ArrayStack implements StackADT { private final static int DEFAULT_CAPACITY = 100;

private int top; private T[] stack; /** * Creates an empty stack using the default capacity. */ public ArrayStack() { this(DEFAULT_CAPACITY); }

/** * Creates an empty stack using the specified capacity. * @param initialCapacity the initial size of the array */ public ArrayStack(int initialCapacity) { top = 0; stack = (T[])(new Object[initialCapacity]); }

/** * Adds the specified element to the top of this stack, expanding * the capacity of the array if necessary. * @param element generic element to be pushed onto stack */ public void push(T element) { if (size() == stack.length) expandCapacity();

stack[top] = element; top++; }

/** * Creates a new array to store the contents of this stack with * twice the capacity of the old one. */ private void expandCapacity() { stack = Arrays.copyOf(stack, stack.length * 2); }

/** * Removes the element at the top of this stack and returns a * reference to it. * @return element removed from top of stack * @throws EmptyCollectionException if stack is empty */ public T pop() throws EmptyCollectionException { if (isEmpty()) throw new EmptyCollectionException("stack");

top--; T result = stack[top]; stack[top] = null;

return result; } /** * Returns a reference to the element at the top of this stack. * The element is not removed from the stack. * @return element on top of stack * @throws EmptyCollectionException if stack is empty */ public T peek() throws EmptyCollectionException { if (isEmpty()) throw new EmptyCollectionException("stack");

return stack[top-1]; }

/** * Returns true if this stack is empty and false otherwise. * @return true if this stack is empty */ public boolean isEmpty() { // To be completed as a Programming Project } /** * Returns the number of elements in this stack. * @return the number of elements in the stack */ public int size() { // To be completed as a Programming Project }

/** * Returns a string representation of this stack. * @return a string representation of the stack */ public String toString() { // To be completed as a Programming Project } }