ArrayListStack

package prep_27_stack;

import java.util.ArrayList;
import java.util.NoSuchElementException;

public class ArrayListStack implements StackI {
	private ArrayList<Object> stack;

	/**
	 * Constructs an empty stack.
	 */
	public ArrayListStack() {
		stack = new ArrayList<Object>();
	}

	/**
	 * Adds an element to the top of the stack.
	 *
	 * @param element the element to add
	 */
	@Override
	public void push(Object element) {
		stack.add(element);
	}

	/**
	 * Removes the element from the top of the stack.
	 *
	 * @return the removed element
	 */
	@Override
	public Object pop() {
		if (stack.size() - 1 < 0) {
			throw new NoSuchElementException();
		}
		Object element = stack.get(stack.size() - 1);
		stack.remove(stack.size() - 1);
		return element;
	}

	/**
	 * Returns the element from the top of the stack. The stack is unchanged
	 *
	 * @return the element from the top of the stack
	 */
	@Override
	public Object peek() {
		if (stack.size() - 1 < 0) {
			throw new NoSuchElementException();
		}
		Object element = stack.get(stack.size() - 1);
		return element;
	}

	/**
	 * Checks whether this stack is empty.
	 *
	 * @return true if the stack is empty
	 */
	@Override
	public boolean isEmpty() {
		if (stack.size() > 0) {
			return false;
		} else {
			return true;
		}
	}

	/**
	 * The number of elements on the stack.
	 *
	 * @return the number of elements on the stack
	 */
	@Override
	public int size() {
		return stack.size();
	}
}