Stack.java

// Generic stack using Object[] - Pages 125-127
package org.effectivejava.examples.chapter05.item26.secondtechnqiue;

import java.util.Arrays;

public class Stack<E> {
	private Object[] elements;
	private int size = 0;
	private static final int DEFAULT_INITIAL_CAPACITY = 16;

	public Stack() {
		elements = new Object[DEFAULT_INITIAL_CAPACITY];
	}

	public void push(E e) {
		ensureCapacity();
		elements[size++] = e;
	}

	// Appropriate suppression of unchecked warning
	public E pop() {
		if (size == 0)
			throw new EmptyStackException();

		// push requires elements to be of type E, so cast is correct
		@SuppressWarnings("unchecked")
		E result = (E) elements[--size];

		elements[size] = null; // Eliminate obsolete reference
		return result;
	}

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

	private void ensureCapacity() {
		if (elements.length == size)
			elements = Arrays.copyOf(elements, 2 * size + 1);
	}

	// Little program to exercise our generic Stack
	public static void main(String[] args) {
		Stack<String> stack = new Stack<String>();
		for (String arg : args)
			stack.push(arg);
		while (!stack.isEmpty())
			System.out.println(stack.pop().toUpperCase());
	}
}