Stack.java

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

import java.util.Arrays;

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

	// The elements array will contain only E instances from push(E).
	// This is sufficient to ensure type safety, but the runtime
	// type of the array won't be E[]; it will always be Object[]!
	@SuppressWarnings("unchecked")
	public Stack() {
		elements = (E[]) new Object[DEFAULT_INITIAL_CAPACITY];
	}

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

	public E pop() {
		if (size == 0)
			throw new EmptyStackException();
		E result = 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());
	}
}