CircularQueue.java

package org.droidplanner.android.utils.collection;

/**
 * Created by Fredia Huya-Kouadio on 1/23/15.
 */
public class CircularQueue<T> {

    private final T[] buffer;
    private int bufferSize;
    private int bufferIndex;

    public CircularQueue(int capacity) {
        buffer = (T[]) new Object[capacity];
        bufferSize = 0;
        bufferIndex = 0;
    }

    private int getAndIncrementIndex() {
        int index = bufferIndex;
        bufferIndex = (bufferIndex + 1) % buffer.length;
        return index;
    }

    private int decrementAndGetIndex() {
        bufferIndex = (buffer.length + bufferIndex - 1) % buffer.length;
        return bufferIndex;
    }

    public int capacity() {
        return buffer.length;
    }

    public void clear() {
        bufferSize = 0;
        bufferIndex = 0;

        for (int i = 0; i < buffer.length; i++) {
            buffer[i] = null;
        }
    }

    public int size() {
        return bufferSize;
    }

    public boolean isEmpty() {
        return bufferSize == 0;
    }

    public void add(T item) {
        buffer[getAndIncrementIndex()] = item;
        bufferSize++;
    }

    public T poll() {
        if (isEmpty())
            return null;

        int index = decrementAndGetIndex();
        T item = buffer[index];
        buffer[index] = null;
        bufferSize--;
        return item;
    }
}