org.apache.commons.collections.buffer.UnboundedFifoBuffer Maven / Gradle / Ivy
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Provides a single jar containing all JAITools modules which you can
use instead of including individual modules in your project. Note:
It does not include the Jiffle scripting language or Jiffle image
operator.
/* ====================================================================
* The Apache Software License, Version 1.1
*
* Copyright (c) 2002-2004 The Apache Software Foundation. All rights
* reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* 3. The end-user documentation included with the redistribution, if
* any, must include the following acknowledgement:
* "This product includes software developed by the
* Apache Software Foundation (http://www.apache.org/)."
* Alternately, this acknowledgement may appear in the software itself,
* if and wherever such third-party acknowledgements normally appear.
*
* 4. The names "The Jakarta Project", "Commons", and "Apache Software
* Foundation" must not be used to endorse or promote products derived
* from this software without prior written permission. For written
* permission, please contact [email protected].
*
* 5. Products derived from this software may not be called "Apache"
* nor may "Apache" appear in their names without prior written
* permission of the Apache Software Foundation.
*
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
* ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
* ====================================================================
*
* This software consists of voluntary contributions made by many
* individuals on behalf of the Apache Software Foundation. For more
* information on the Apache Software Foundation, please see
*
* 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.
*
* @since Commons Collections 3.0 (previously in main package v2.1)
* @version $Revision: 1.6 $ $Date: 2004/01/14 21:43:08 $
*
* @author Avalon
* @author Federico Barbieri
* @author Berin Loritsch
* @author Paul Jack
* @author Stephen Colebourne
*/
public class UnboundedFifoBuffer extends AbstractCollection implements Buffer {
protected Object[] buffer;
protected int head;
protected int 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");
}
buffer = new Object[initialSize + 1];
head = 0;
tail = 0;
}
/**
* Returns the number of elements stored in the buffer.
*
* @return this buffer's size
*/
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
*/
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
*/
public boolean add(final Object obj) {
if (obj == null) {
throw new NullPointerException("Attempted to add null object to buffer");
}
if (size() + 1 >= buffer.length) {
Object[] tmp = 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
*/
public Object 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
*/
public Object remove() {
if (isEmpty()) {
throw new BufferUnderflowException("The buffer is already empty");
}
Object 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
*/
public Iterator iterator() {
return new Iterator() {
private int index = head;
private int lastReturnedIndex = -1;
public boolean hasNext() {
return index != tail;
}
public Object next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
lastReturnedIndex = index;
index = increment(index);
return buffer[lastReturnedIndex];
}
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);
}
};
}
}
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