// GenericsNote: Converted.
/*
* Copyright 2002-2004 The Apache Software Foundation
*
* 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 org.apache.commons.collections15.buffer;
import java.util.AbstractCollection;
import java.util.Iterator;
import java.util.NoSuchElementException;
import org.apache.commons.collections15.Buffer;
import org.apache.commons.collections15.BufferUnderflowException;
/**
* UnboundedFifoBuffer is a very efficient buffer implementation. According to
* performance testing, it exhibits a constant access time, but it also
* outperforms ArrayList when used for the same purpose.
* <p/>
* The removal order of an <code>UnboundedFifoBuffer</code> is based on the
* insertion order; elements are removed in the same order in which they were
* added. The iteration order is the same as the removal order.
* <p/>
* The {@link #remove()} and {@link #get()} operations perform in constant time.
* The {@link #add(Object)} operation performs in amortized constant time. All
* other operations perform in linear time or worse.
* <p/>
* Note that this implementation is not synchronized. The following can be used
* to provide synchronized access to your <code>UnboundedFifoBuffer</code>:
*
* <pre>
* Buffer fifo = BufferUtils.synchronizedBuffer(new UnboundedFifoBuffer());
* </pre>
* <p/>
* This buffer prevents null objects from being added.
* <p/>
* This class is Serializable from Commons Collections 3.1.
*
* @author Avalon
* @author Federico Barbieri
* @author Berin Loritsch
* @author Paul Jack
* @author Matt Hall, John Watkinson, Stephen Colebourne
* @version $Revision: 1.1 $ $Date: 2005/10/11 17:05:20 $
* @since Commons Collections 3.0 (previously in main package v2.1)
*/
public class UnboundedFifoBuffer<E> extends AbstractCollection<E>
implements Buffer<E> {
/**
* The array of objects in the buffer.
*/
protected transient E[] buffer;
/**
* The current head index.
*/
protected transient int head;
/**
* The current tail index.
*/
protected transient int tail;
/**
* Constructs an UnboundedFifoBuffer with the default number of elements. It
* is exactly the same as performing the following:
* <p/>
*
* <pre>
* new UnboundedFifoBuffer(32);
* </pre>
*/
public UnboundedFifoBuffer() {
this(32);
}
/**
* Constructs an UnboundedFifoBuffer with the specified number of elements.
* The integer must be a positive integer.
*
* @param initialSize
* the initial size of the buffer
* @throws IllegalArgumentException
* if the size is less than 1
*/
public UnboundedFifoBuffer(int initialSize) {
if (initialSize <= 0) {
throw new IllegalArgumentException(
"The size must be greater than 0");
}
buffer = (E[]) new Object[initialSize + 1];
head = 0;
tail = 0;
}
// -----------------------------------------------------------------------
/**
* Returns the number of elements stored in the buffer.
*
* @return this buffer's size
*/
@Override
public int size() {
int size = 0;
if (tail < head) {
size = buffer.length - head + tail;
} else {
size = tail - head;
}
return size;
}
/**
* Returns true if this buffer is empty; false otherwise.
*
* @return true if this buffer is empty
*/
@Override
public boolean isEmpty() {
return (size() == 0);
}
/**
* Adds the given element to this buffer.
*
* @param obj
* the element to add
* @return true, always
* @throws NullPointerException
* if the given element is null
*/
@Override
public boolean add(final E obj) {
if (obj == null) {
throw new NullPointerException(
"Attempted to add null object to buffer");
}
if (size() + 1 >= buffer.length) {
E[] tmp = (E[]) new Object[((buffer.length - 1) * 2) + 1];
int j = 0;
for (int i = head; i != tail;) {
tmp[j] = buffer[i];
buffer[i] = null;
j++;
i++;
if (i == buffer.length) {
i = 0;
}
}
buffer = tmp;
head = 0;
tail = j;
}
buffer[tail] = obj;
tail++;
if (tail >= buffer.length) {
tail = 0;
}
return true;
}
/**
* Returns the next object in the buffer.
*
* @return the next object in the buffer
* @throws BufferUnderflowException
* if this buffer is empty
*/
@Override
public E get() {
if (isEmpty()) {
throw new BufferUnderflowException("The buffer is already empty");
}
return buffer[head];
}
/**
* Removes the next object from the buffer
*
* @return the removed object
* @throws BufferUnderflowException
* if this buffer is empty
*/
@Override
public E remove() {
if (isEmpty()) {
throw new BufferUnderflowException("The buffer is already empty");
}
E element = buffer[head];
if (null != element) {
buffer[head] = null;
head++;
if (head >= buffer.length) {
head = 0;
}
}
return element;
}
/**
* Increments the internal index.
*
* @param index
* the index to increment
* @return the updated index
*/
private int increment(int index) {
index++;
if (index >= buffer.length) {
index = 0;
}
return index;
}
/**
* Decrements the internal index.
*
* @param index
* the index to decrement
* @return the updated index
*/
private int decrement(int index) {
index--;
if (index < 0) {
index = buffer.length - 1;
}
return index;
}
/**
* Returns an iterator over this buffer's elements.
*
* @return an iterator over this buffer's elements
*/
@Override
public Iterator<E> iterator() {
return new Iterator<E>() {
private int index = head;
private int lastReturnedIndex = -1;
@Override
public boolean hasNext() {
return index != tail;
}
@Override
public E next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
lastReturnedIndex = index;
index = increment(index);
return buffer[lastReturnedIndex];
}
@Override
public void remove() {
if (lastReturnedIndex == -1) {
throw new IllegalStateException();
}
// First element can be removed quickly
if (lastReturnedIndex == head) {
UnboundedFifoBuffer.this.remove();
lastReturnedIndex = -1;
return;
}
// Other elements require us to shift the subsequent elements
int i = lastReturnedIndex + 1;
while (i != tail) {
if (i >= buffer.length) {
buffer[i - 1] = buffer[0];
i = 0;
} else {
buffer[i - 1] = buffer[i];
i++;
}
}
lastReturnedIndex = -1;
tail = decrement(tail);
buffer[tail] = null;
index = decrement(index);
}
};
}
}