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;
}
