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
 *  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 ) {
      } 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;

   private List<T> queue;
   private int mostRecentItem;
   private int size;


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