How to extend the collections framework
/*
This program is a part of the companion code for Core Java 8th ed.
(http://horstmann.com/corejava)
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
import java.util.AbstractQueue;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Queue;
/**
* This program demonstrates how to extend the collections framework.
* @version 1.20 2007-05-16
* @author Cay Horstmann
*/
public class CircularArrayQueueTest
{
public static void main(String[] args)
{
Queue<String> q = new CircularArrayQueue<String>(5);
q.add("Amy");
q.add("Bob");
q.add("Carl");
q.add("Deedee");
q.add("Emile");
q.remove();
q.add("Fifi");
q.remove();
for (String s : q) System.out.println(s);
}
}
/**
A first-in, first-out bounded collection.
*/
class CircularArrayQueue<E> extends AbstractQueue<E>
{
/**
Constructs an empty queue.
@param capacity the maximum capacity of the queue
*/
public CircularArrayQueue(int capacity)
{
elements = new Object[capacity];
count = 0;
head = 0;
tail = 0;
}
public boolean offer(E newElement)
{
assert newElement != null;
if (count < elements.length)
{
elements[tail] = newElement;
tail = (tail + 1) % elements.length;
count++;
modcount++;
return true;
}
else
return false;
}
public E poll()
{
if (count == 0) return null;
E r = peek();
head = (head + 1) % elements.length;
count--;
modcount++;
return r;
}
@SuppressWarnings("unchecked")
public E peek()
{
if (count == 0) return null;
return (E) elements[head];
}
public int size()
{
return count;
}
public Iterator<E> iterator()
{
return new QueueIterator();
}
private class QueueIterator implements Iterator<E>
{
public QueueIterator()
{
modcountAtConstruction = modcount;
}
@SuppressWarnings("unchecked")
public E next()
{
if (!hasNext()) throw new NoSuchElementException();
E r = (E) elements[(head + offset) % elements.length];
offset++;
return r;
}
public boolean hasNext()
{
if (modcount != modcountAtConstruction)
throw new ConcurrentModificationException();
return offset < count;
}
public void remove()
{
throw new UnsupportedOperationException();
}
private int offset;
private int modcountAtConstruction;
}
private Object[] elements;
private int head;
private int tail;
private int count;
private int modcount;
}
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