Rotating queue of fixed size. : Queue « Collections Data Structure « Java






Rotating queue of fixed size.

        
/*
 *  Copyright 2009 Ancora Research Group.
 * 
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 * 
 *       http://www.apache.org/licenses/LICENSE-2.0
 * 
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *  under the License.
 */

//package org.ancora.SharedLibrary.DataStructures;

import java.util.ArrayList;
import java.util.List;

/**
 * Rotating queue of fixed size.
 *
 * @author Joao Bispo
 */
public class RotatingQueue<T> {

   public RotatingQueue(int capacity) {
      size = capacity;
      queue = new ArrayList<T>(capacity);
      mostRecentItem = capacity-1;
   }

   /**
    * Inserts an element to the head of the queue, pushing all other elements
    * one position forward.
    *
    * @param element
    */
   public void insertElement(T element) {
      //Get index
      mostRecentItem = advancePointer(mostRecentItem);

      //Check if list already has an element
      if(queue.size() == mostRecentItem ) {
         queue.add(element);
      } else {
         queue.set(mostRecentItem, element);
      }
   }

   public T getElement(int index) {
      // Normalize index to size of queue
      index = index % size;

      // Translate wanted index to queue index
      int queueIndex = mostRecentItem - index;
      // If negative, add size
      if(queueIndex < 0) {
         queueIndex += size;
      }

      // Check if element already exists in queue
      if(queueIndex < queue.size()) {
         return queue.get(queueIndex);
      } else {
         return null;
      }
   }

   public int size() {
      return size;
   }

   private int advancePointer(int oldPointer) {
      int pointer = oldPointer+1;
      if(pointer < size) {
         return pointer;
      } else {
         return 0;
      }
   }

   ///
   // INSTANCE VARIABLES
   ///
   private List<T> queue;
   private int mostRecentItem;
   private int size;
}

   
    
    
    
    
    
    
    
  








Related examples in the same category

1.Priority queuePriority queue
2.Queue data structureQueue data structure
3.Convert a Queue to a List
4.Create a queue using LinkedList class
5.Simple Queue (FIFO) based on LinkedList
6.The Generic Queue Class
7.Blocking Queue
8.Circular Queue
9.Circular Queue extends AbstractList
10.How to extend the collections framework
11.An unbounded {@link TransferQueue} based on linked nodes.
12.This class implements the data structures necessary for an ArrayQueue
13.A circular queue from mina
14.An unbounded TransferQueue based on linked nodes.
15.Allows threads to communicate asynchronously by putting messages into and reading messages out of a synchronized queue.