import java.util.Iterator;

import java.util.NoSuchElementException;

/**

* Stack implemented using dynamically sized array.

* @author James Pope

* @param <Type>

*/

public class Stack <Type> implements Iterable<Type>

{

private static final int DEFAULT_CAPACITY = 8;

private Type[] items;

private int size;

public Stack()

{

this.items = (Type[])new Object[DEFAULT_CAPACITY];

this.size = 0;

}

public void push(Type item)

{

// If not eough room , expand

if( this.size == this.items.length )

{

grow();

}

this.items[size] = item;

this.size++;

}

public Type pop()

{

if( this.isEmpty() )

{

throw new IllegalArgumentException("No item to pop");

}

this.size--;

Type item = this.items[size];

this.items[size] = null; // prevent loitering

return item;

}

public Type peek()

{

return this.items[size-1];

}

public int size()

{

return this.size;

}

public boolean isEmpty()

{

return this.size == 0;

}

private void grow()

{

Type[] newItems = (Type[])new Object[this.items.length*2];

System.arraycopy(this.items, 0, newItems, 0, this.items.length);

this.items = newItems;

}

@Override

public String toString()

{

StringBuilder buf = new StringBuilder();

buf.append("[");

for (int i = 0; i < this.size; i++)

{

Type item = items[i];

if( i != 0 ) buf.append(", ");

buf.append( item.toString() );

}

buf.append("]");

return buf.toString();

}

public Iterator<Type> iterator()

{

return new Iterator()

{

private int currentIndex = size - 1;

public boolean hasNext()

{

return currentIndex >= 0;

}

public Object next()

{

if( currentIndex < 0 )

{

throw new NoSuchElementException("No more elements");

}

return items[currentIndex--];

}

public void remove()

{

throw new UnsupportedOperationException("Not supported yet.");

}

};

}

}