FIFOQueue.java

/*
 *    GeoTools - The Open Source Java GIS Toolkit
 *    http://geotools.org
 *
 *    (C) 2002-2008, Open Source Geospatial Foundation (OSGeo)
 *
 *    This library is free software; you can redistribute it and/or
 *    modify it under the terms of the GNU Lesser General Public
 *    License as published by the Free Software Foundation;
 *    version 2.1 of the License.
 *
 *    This library 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
 *    Lesser General Public License for more details.
 */
package org.geotools.graph.util;

import java.util.Collection;
import java.util.Iterator;
import java.util.NoSuchElementException;

public class FIFOQueue implements Collection, Queue {
   private static final int DEFAULT_SIZE = 10;
   
   private Object[] m_values;
   private int m_in;
   private int m_out;
   private boolean m_full;
   private boolean m_empty;
   
   public FIFOQueue() {
     this(DEFAULT_SIZE);  
     m_full = false;
   }
   
   public FIFOQueue(int size) {
     m_values = new Object[size];
     clear();
     
   }
   
   public void enq(Object element) {
     if (m_full) throw new IllegalStateException("Queue full."); 
     m_empty = false;
     
     m_values[m_in++] = element;
     if (m_in == m_values.length) m_in = 0;
     m_full = m_in == m_out;
   }
   
   public Object deq() {
     if (m_empty) throw new NoSuchElementException("Heap empty.");
     m_full = false;
     
     Object o = m_values[m_out];
     m_values[m_out++] = null;
     
     if (m_out == m_values.length) m_out= 0;
     m_empty = m_in == m_out;
     
     return(o);
   }

  public int size() {
    if (m_empty) return(0);
    if (m_full) return(m_values.length);
    
    int size = 0;
    for (int i = m_out; i < m_values.length;i++, size++) {
      if (i == m_in) return(size);      
    }
    
    for (int i = 0; i < m_in; i++, size++);
    
    return(size);
  }

  public void clear() {
    m_in = 0;
    m_out = 0;
    m_full = false;
    m_empty = true;
  }

  
  public boolean isEmpty() {
    return(m_empty);
  }
  
  public boolean isFull() {
    return(m_full);  
  }

  public Object[] toArray() {
    return(m_values);  
  }

  public boolean add(Object o) {
    enq(o);
    return(true);
  }

  public boolean contains(Object o) {
    for (int i = 0; i < m_values.length; i++) {
      if (m_values[i] != null && m_values[i].equals(o)) return(true);  
    }
    return(false);
  }

  public boolean remove(Object o) {
    throw new UnsupportedOperationException("remove(Object)");
  }

  public boolean addAll(Collection c) {
    for (Iterator itr = c.iterator(); itr.hasNext();) {
      enq(itr.next());  
    }
    return(true);
  }

  public boolean containsAll(Collection c) {
    for (Iterator itr = c.iterator(); itr.hasNext();) {
      if (!contains(itr.next())) return(false);
    }
    return(true);
  }

  public boolean removeAll(Collection c) {
    throw new UnsupportedOperationException("removeAll(Collection)");
  }

  public boolean retainAll(Collection c) {
    throw new UnsupportedOperationException("retainAll(Collection)");
  }

  public Iterator iterator() {
    return(new QueueIterator());
  }

  public Object[] toArray(Object[] a) {
    int size = size();
    if (a.length < size) {
      a = (Object[])java.lang.reflect.Array.newInstance(
        a.getClass().getComponentType(), size
      );
    }
    
    int j = 0;
    for (int i = m_out; i < m_values.length; i++, j++) {
      if (i == m_in) {
        if (j < a.length) a[j] = null;
        return(a);
      }
      a[j] = m_values[i];
    }
    
    for (int i = 0; i < m_out; i++, j++) {
      a[j] = m_values[i];  
    }
    
    if (j < a.length) a[j] = null;
    
    return(a);
  }
  
  public class QueueIterator implements Iterator {
    int m_index = m_out;
    
    private QueueIterator() {}
    
    public void remove() {
      throw new UnsupportedOperationException("remove()");  
    }

    public boolean hasNext() {
      return(m_index != m_in);
    }

    public Object next() {
      Object o = m_values[m_index++];
      if (m_index == m_values.length) m_index = 0;
      return(o);
    }
  }
  
  //package level visibility data methods for testing
  int in() { return(m_in); }
  
  int out() { return(m_out); }
  
  Object[] values() { return(m_values); }
  
}