10分間で作った

Stack.java

package net.flourity.lib;

import java.util.Arrays;
import java.util.NoSuchElementException;

public class Stack<E>
{
	private Object[] elements;
	private int size;
	
	public Stack()
	{
		this(16);
	}
	
	public Stack(int initialCapacity)
	{
		elements = new Object[initialCapacity];
	}
	
	public void push(E e)
	{
		ensureCapacity(size+1);
		elements[size++] = e;
	}
	
	public E pop()
	{
		if(size==0) throw new NoSuchElementException();
		@SuppressWarnings("unchecked")
		E res = (E)elements[size-1];
		elements[--size] = null;
		return res;
	}
	
	public E peek()
	{
		if(size==0) throw new NoSuchElementException();
		@SuppressWarnings("unchecked")
		E res = (E)elements[size-1];
		return res;
	}
	
	public void ensureCapacity(int minCapacity)
	{
		int oldCapacity = elements.length;
		if(oldCapacity<minCapacity)
		{
			int newCapacity = oldCapacity << 1;
			if(newCapacity<minCapacity) newCapacity = minCapacity;
			elements = Arrays.copyOf(elements, newCapacity);
		}
	}
	
	public int size()
	{
		return size;
	}
	
	public boolean isEmpty()
	{
		return size==0;
	}
	
	
}