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package horstmann.ch08_queue;
import java.util.AbstractCollection;
import java.util.ArrayList;
import java.util.Iterator;
/**
A first-in, first-out bounded collection of objects.
*/
public class BoundedQueue<E> extends AbstractCollection<E>
{
/**
Constructs an empty queue.
@param capacity the maximum capacity of the queue
<p><b>Precondition:</b> capacity > 0</p>
*/
public BoundedQueue(int capacity)
{
elements = new ArrayList<E>(capacity);
count = 0;
head = 0;
tail = 0;
}
public Iterator<E> iterator()
{
return new
Iterator<E>()
{
public boolean hasNext()
{
return visited < count;
}
public E next()
{
int index = (head + visited) % elements.size();
E r = elements.get(index);
visited++;
return r;
}
public void remove()
{
throw new UnsupportedOperationException();
}
private int visited = 0;
};
}
/**
Remove object at head.
@return the object that has been removed from the queue
<p><b>Precondition:</b> size() > 0</p>
*/
public E remove()
{
E r = elements.get(head);
head = (head + 1) % elements.size();
count--;
return r;
}
/**
Append an object at tail.
@param anObject the object to be appended
@return true since this operation modifies the queue.
(This is a requirement of the collections framework.)
<p><b>Precondition:</b> !isFull()</p>
*/
public boolean add(E anObject)
{
elements.set(tail,anObject);
tail = (tail + 1) % elements.size();
count++;
return true;
}
public int size()
{
return count;
}
/**
Checks whether this queue is full.
@return true if the queue is full
*/
public boolean isFull()
{
return count == elements.size();
}
/**
Gets object at head.
@return the object that is at the head of the queue
<p><b>Precondition:</b> size() > 0</p>
*/
public E peek()
{
return elements.get(head);
}
private ArrayList<E> elements;
private int head;
private int tail;
private int count;
}
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