/*
* 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.collections;
import java.util.AbstractCollection;
import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* The BoundedFifoBuffer is a very efficient implementation of
* Buffer that does not alter the size of the buffer at runtime.
* <p>
* The removal order of a <code>BoundedFifoBuffer</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 #add(Object)}, {@link #remove()} and {@link #get()} operations
* all perform in 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>BoundedFifoBuffer</code>:
* <pre>
* Buffer fifo = BufferUtils.synchronizedBuffer(new BoundedFifoBuffer());
* </pre>
* <p>
* This buffer prevents null objects from being added.
*
* @deprecated Moved to buffer subpackage. Due to be removed in v4.0.
* @since 2.1
* @version $Revision: 155406 $ $Date: 2005-02-26 12:55:26 +0000 (Sat, 26 Feb 2005) $
*
* @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[] m_elements;
private int m_start = 0;
private int m_end = 0;
private boolean m_full = false;
private final int maxElements;
/**
* Constructs a new <code>BoundedFifoBuffer</code> big enough to hold
* 32 elements.
*/
public BoundedFifoBuffer() {
this(32);
}
/**
* Constructs a new <code>BoundedFifoBuffer</code> 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");
}
m_elements = new Object[size];
maxElements = m_elements.length;
}
/**
* Constructs a new <code>BoundedFifoBuffer</code> 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 (m_end < m_start) {
size = maxElements - m_start + m_end;
} else if (m_end == m_start) {
size = (m_full ? maxElements : 0);
} else {
size = m_end - m_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 <code>true</code> 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() {
m_full = false;
m_start = 0;
m_end = 0;
Arrays.fill(m_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 (m_full) {
throw new BufferOverflowException("The buffer cannot hold more than " + maxElements + " objects.");
}
m_elements[m_end++] = element;
if (m_end >= maxElements) {
m_end = 0;
}
if (m_end == m_start) {
m_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 m_elements[m_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 = m_elements[m_start];
if (null != element) {
m_elements[m_start++] = null;
if (m_start >= maxElements) {
m_start = 0;
}
m_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 = m_start;
private int lastReturnedIndex = -1;
private boolean isFirst = m_full;
public boolean hasNext() {
return isFirst || (index != m_end);
}
public Object next() {
if (!hasNext()) throw new NoSuchElementException();
isFirst = false;
lastReturnedIndex = index;
index = increment(index);
return m_elements[lastReturnedIndex];
}
public void remove() {
if (lastReturnedIndex == -1) throw new IllegalStateException();
// First element can be removed quickly
if (lastReturnedIndex == m_start) {
BoundedFifoBuffer.this.remove();
lastReturnedIndex = -1;
return;
}
// Other elements require us to shift the subsequent elements
int i = lastReturnedIndex + 1;
while (i != m_end) {
if (i >= maxElements) {
m_elements[i - 1] = m_elements[0];
i = 0;
} else {
m_elements[i - 1] = m_elements[i];
i++;
}
}
lastReturnedIndex = -1;
m_end = decrement(m_end);
m_elements[m_end] = null;
m_full = false;
index = decrement(index);
}
};
}
}