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/* ====================================================================
* 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"
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*
* 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 a BoundedFifoBuffer 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 #add(Object)}, {@link #remove()} and {@link #get()} operations
* all perform in 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 BoundedFifoBuffer:
*
* Buffer fifo = BufferUtils.synchronizedBuffer(new BoundedFifoBuffer());
*
*
* 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 Berin Loritsch
* @author Paul Jack
* @author Stephen Colebourne
* @author Herve Quiroz
*/
public class BoundedFifoBuffer extends AbstractCollection
implements Buffer, BoundedCollection {
private final Object[] elements;
private int start = 0;
private int end = 0;
private boolean full = false;
private final int maxElements;
/**
* Constructs a new BoundedFifoBuffer big enough to hold
* 32 elements.
*/
public BoundedFifoBuffer() {
this(32);
}
/**
* Constructs a new BoundedFifoBuffer big enough to hold
* the specified number of elements.
*
* @param size the maximum number of elements for this fifo
* @throws IllegalArgumentException if the size is less than 1
*/
public BoundedFifoBuffer(int size) {
if (size <= 0) {
throw new IllegalArgumentException("The size must be greater than 0");
}
elements = new Object[size];
maxElements = elements.length;
}
/**
* Constructs a new BoundedFifoBuffer big enough to hold all
* of the elements in the specified collection. That collection's
* elements will also be added to the buffer.
*
* @param coll the collection whose elements to add, may not be null
* @throws NullPointerException if the collection is null
*/
public BoundedFifoBuffer(Collection coll) {
this(coll.size());
addAll(coll);
}
/**
* Returns the number of elements stored in the buffer.
*
* @return this buffer's size
*/
public int size() {
int size = 0;
if (end < start) {
size = maxElements - start + end;
} else if (end == start) {
size = (full ? maxElements : 0);
} else {
size = end - start;
}
return size;
}
/**
* Returns true if this buffer is empty; false otherwise.
*
* @return true if this buffer is empty
*/
public boolean isEmpty() {
return size() == 0;
}
/**
* Returns true if this collection is full and no new elements can be added.
*
* @return true if the collection is full
*/
public boolean isFull() {
return size() == maxElements;
}
/**
* Gets the maximum size of the collection (the bound).
*
* @return the maximum number of elements the collection can hold
*/
public int maxSize() {
return maxElements;
}
/**
* Clears this buffer.
*/
public void clear() {
full = false;
start = 0;
end = 0;
Arrays.fill(elements, null);
}
/**
* Adds the given element to this buffer.
*
* @param element 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(Object element) {
if (null == element) {
throw new NullPointerException("Attempted to add null object to buffer");
}
if (full) {
throw new BufferOverflowException("The buffer cannot hold more than " + maxElements + " objects.");
}
elements[end++] = element;
if (end >= maxElements) {
end = 0;
}
if (end == start) {
full = true;
}
return true;
}
/**
* Returns the least recently inserted element in this buffer.
*
* @return the least recently inserted element
* @throws BufferUnderflowException if the buffer is empty
*/
public Object get() {
if (isEmpty()) {
throw new BufferUnderflowException("The buffer is already empty");
}
return elements[start];
}
/**
* Removes the least recently inserted element from this buffer.
*
* @return the least recently inserted element
* @throws BufferUnderflowException if the buffer is empty
*/
public Object remove() {
if (isEmpty()) {
throw new BufferUnderflowException("The buffer is already empty");
}
Object element = elements[start];
if (null != element) {
elements[start++] = null;
if (start >= maxElements) {
start = 0;
}
full = false;
}
return element;
}
/**
* Increments the internal index.
*
* @param index the index to increment
* @return the updated index
*/
private int increment(int index) {
index++;
if (index >= maxElements) {
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 = maxElements - 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 = start;
private int lastReturnedIndex = -1;
private boolean isFirst = full;
public boolean hasNext() {
return isFirst || (index != end);
}
public Object next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
isFirst = false;
lastReturnedIndex = index;
index = increment(index);
return elements[lastReturnedIndex];
}
public void remove() {
if (lastReturnedIndex == -1) {
throw new IllegalStateException();
}
// First element can be removed quickly
if (lastReturnedIndex == start) {
BoundedFifoBuffer.this.remove();
lastReturnedIndex = -1;
return;
}
// Other elements require us to shift the subsequent elements
int i = lastReturnedIndex + 1;
while (i != end) {
if (i >= maxElements) {
elements[i - 1] = elements[0];
i = 0;
} else {
elements[i - 1] = elements[i];
i++;
}
}
lastReturnedIndex = -1;
end = decrement(end);
elements[end] = null;
full = false;
index = decrement(index);
}
};
}
}