Chapter 19 Exercise 1, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

19.1 (Revising Listing 19.1)
Revise the GenericStack class in Listing 19.1 to implement it using an array
rather than an ArrayList. You should check the array size before adding a new
element to the stack. If the array is full, create a new array that doubles the
current array size and copy the elements from the current array to the new array.

import java.util.Arrays;

public class Exercise_01 {

    public static void main(String[] args) {

        GenericStack<Integer> numberStack = new GenericStack<>();

        for (int i = 0; i < 10000; i++) {
            numberStack.push(i);
        }

        System.out.println("Current Size" + numberStack.getSize());
        System.out.println("Is stack empty? " + numberStack.isEmpty());
        System.out.println("Pop: " + numberStack.pop());
        System.out.println("Pop: " + numberStack.pop());
        System.out.println("Current Size " + numberStack.getSize());
        System.out.println("Popping all from stack...");

    }

    static private class GenericStack<E> {

        private int capacity = 100;
        private int size;
        private E[] array = (E[])new Object[capacity];

        GenericStack() {

        }

        public int getSize() {
            return size;
        }

        public E peek() {
            if (size == 0)
                return null;
            else
                return array[size - 1];
        }

        public void push(E o) {
            array[size++] = o;
            if (size == capacity) {
                E[] tmp = (E[])new Object[capacity *= 2];
                System.arraycopy(array, 0, tmp, 0, array.length);
                array = tmp;
            }
        }

        public E pop() {
            if (size == 0)
                return null;
            else
                return array[--size];
        }

        public boolean isEmpty() {
            return size == 0;
        }

        @Override
        public String toString() {
            return "stack: " + Arrays.toString(array);
        }
    }
}