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reactive4java developed by David Karnok
There is a newer version: 0.98.1
/*
 * Copyright 2011-2013 David Karnok
 *
 * 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.
 */

package hu.akarnokd.reactive4java.util;

import java.util.NoSuchElementException;

/**
 * A simple circular buffer with absolute indices.
 * @author akarnokd, 2011.02.04.
 * @param  the contained element type
 */
public class CircularBuffer {
    /** The buffer. */
    final Object[] buffer;
    /** The head pointer. */
    int head;
    /** The tail pointer. */
    int tail;
    /**
     * Construct a new circular buffer.
     * @param size the buffer size
     */
    public CircularBuffer(int size) {
        buffer = new Object[size];
    }
    /**
     * Add a new value to the buffer.
     * If the buffer would overflow, it automatically removes the current head element.
     * @param value the value
     */
    public void add(T value) {
        buffer[(tail++) % buffer.length] = value;
        if (size() > buffer.length) {
            head++;
        }
    }
    /**
     * Retrieve a buffer element based on an absolute index.
     * @param index the absolute index
     * @return the value
     */
    @SuppressWarnings("unchecked")
    public T get(int index) {
        if (index < head) {
            throw new IllegalArgumentException("read before head");
        }
        if (index >= tail) {
            throw new IllegalArgumentException("read after tail");
        }
        return (T)buffer[index % buffer.length];
    }
    /**
     * @return Takes the head of the buffer.
     */
    @SuppressWarnings("unchecked")
    public T take() {
        if (tail == head) {
            throw new NoSuchElementException();
        }
        int idx = head++ % buffer.length;
        T value = (T)buffer[idx];
        buffer[idx] = null;
        return value; 
    }
    /** @return is the buffer empty? */
    public boolean isEmpty() {
        return head == tail;
    }
    /** @return the current size of the buffer. */
    public int size() {
        return tail - head;
    }
    /** @return the current head index. */
    public int head() {
        return head;
    }
    /** @return the current tail index. */
    public int tail() {
        return tail;
    }
}