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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.collections;
import java.util.AbstractCollection;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* 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.
*
* The removal order of an UnboundedFifoBuffer 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.
*
* 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.
*
* Note that this implementation is not synchronized. The following can be
* used to provide synchronized access to your UnboundedFifoBuffer:
*
* Buffer fifo = BufferUtils.synchronizedBuffer(new UnboundedFifoBuffer());
*
*
* This buffer prevents null objects from being added.
*
* @deprecated Moved to buffer subpackage. Due to be removed in v4.0.
* @since Commons Collections 2.1
* @version $Revision$ $Date$
*
* @author Avalon
* @author Federico Barbieri
* @author Berin Loritsch
* @author Paul Jack
* @author Stephen Colebourne
* @author Andreas Schlosser
*
* @deprecated Apache Commons Collections version 3.x is being deprecated from AEMaaCS. The upgraded version 4.4 of Commons Collections is already included as replacement. Customers are advised to upgrade to this version of the library. Please note: the package name was changed to org.apache.commons.collections4. Further note that there are AEM APIs currently exposing the old collections classes; these will be updated in upcoming releases.
*/
@Deprecated(since = "2021-04-30")
public class UnboundedFifoBuffer extends AbstractCollection implements Buffer {
protected Object[] m_buffer;
protected int m_head;
protected int m_tail;
/**
* Constructs an UnboundedFifoBuffer with the default number of elements.
* It is exactly the same as performing the following:
*
*
* new UnboundedFifoBuffer(32);
*
*/
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");
}
m_buffer = new Object[initialSize + 1];
m_head = 0;
m_tail = 0;
}
/**
* Returns the number of elements stored in the buffer.
*
* @return this buffer's size
*/
public int size() {
int size = 0;
if (m_tail < m_head) {
size = m_buffer.length - m_head + m_tail;
} else {
size = m_tail - m_head;
}
return size;
}
/**
* Returns true if this buffer is empty; false otherwise.
*
* @return true if this buffer is empty
*/
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
* @throws BufferOverflowException if this buffer is full
*/
public boolean add(final Object obj) {
if (obj == null) {
throw new NullPointerException("Attempted to add null object to buffer");
}
if (size() + 1 >= m_buffer.length) {
Object[] tmp = new Object[((m_buffer.length - 1) * 2) + 1];
int j = 0;
for (int i = m_head; i != m_tail; ) {
tmp[j] = m_buffer[i];
m_buffer[i] = null;
j++;
i++;
if (i == m_buffer.length) {
i = 0;
}
}
m_buffer = tmp;
m_head = 0;
m_tail = j;
}
m_buffer[m_tail] = obj;
m_tail++;
if (m_tail >= m_buffer.length) {
m_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
*/
public Object get() {
if (isEmpty()) {
throw new BufferUnderflowException("The buffer is already empty");
}
return m_buffer[m_head];
}
/**
* Removes the next object from the buffer
*
* @return the removed object
* @throws BufferUnderflowException if this buffer is empty
*/
public Object remove() {
if (isEmpty()) {
throw new BufferUnderflowException("The buffer is already empty");
}
Object element = m_buffer[m_head];
if (null != element) {
m_buffer[m_head] = null;
m_head++;
if (m_head >= m_buffer.length) {
m_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 >= m_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 = m_buffer.length - 1;
}
return index;
}
/**
* Returns an iterator over this buffer's elements.
*
* @return an iterator over this buffer's elements
*/
public Iterator iterator() {
return new Iterator() {
private int index = m_head;
private int lastReturnedIndex = -1;
public boolean hasNext() {
return index != m_tail;
}
public Object next() {
if (!hasNext())
throw new NoSuchElementException();
lastReturnedIndex = index;
index = increment(index);
return m_buffer[lastReturnedIndex];
}
public void remove() {
if (lastReturnedIndex == -1)
throw new IllegalStateException();
// First element can be removed quickly
if (lastReturnedIndex == m_head) {
UnboundedFifoBuffer.this.remove();
lastReturnedIndex = -1;
return;
}
// Other elements require us to shift the subsequent elements
int i = increment(lastReturnedIndex);
while (i != m_tail) {
m_buffer[decrement(i)] = m_buffer[i];
i = increment(i);
}
lastReturnedIndex = -1;
m_tail = decrement(m_tail);
m_buffer[m_tail] = null;
index = decrement(index);
}
};
}
}