Stack.java

import java.util.EmptyStackException;

public class Stack {
	private ArrayList elementData = new ArrayList();

	public void push(Object o) {
		elementData.add(o);
	}

	public Object pop() {
		if (elementData.size() == 0) {
			throw new EmptyStackException();
		}
		return elementData.remove(elementData.size() - 1);
	}

	public Object peek() {
		return elementData.get(elementData.size() - 1);
	}

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

	public int size() {
		return elementData.size();
	}
}