org.apache.commons.collections.buffer.BoundedFifoBuffer Maven / Gradle / Ivy
/*
* 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.buffer;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.AbstractCollection;
import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;
import java.util.NoSuchElementException;
import org.apache.commons.collections.BoundedCollection;
import org.apache.commons.collections.Buffer;
import org.apache.commons.collections.BufferOverflowException;
import org.apache.commons.collections.BufferUnderflowException;
/**
* The BoundedFifoBuffer is a very efficient implementation of
* Buffer that is of a fixed size.
*
* 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.
*
* This class is Serializable from Commons Collections 3.1.
*
* @since Commons Collections 3.0 (previously in main package v2.1)
* @version $Revision: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $
*
* @author Avalon
* @author Berin Loritsch
* @author Paul Jack
* @author Stephen Colebourne
* @author Herve Quiroz
*/
public class BoundedFifoBuffer extends AbstractCollection
implements Buffer, BoundedCollection, Serializable {
/** Serialization version */
private static final long serialVersionUID = 5603722811189451017L;
/** Underlying storage array */
private transient Object[] elements;
/** Array index of first (oldest) buffer element */
private transient int start = 0;
/**
* Index mod maxElements of the array position following the last buffer
* element. Buffer elements start at elements[start] and "wrap around"
* elements[maxElements-1], ending at elements[decrement(end)].
* For example, elements = {c,a,b}, start=1, end=1 corresponds to
* the buffer [a,b,c].
*/
private transient int end = 0;
/** Flag to indicate if the buffer is currently full. */
private transient boolean full = false;
/** Capacity of the buffer */
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);
}
//-----------------------------------------------------------------------
/**
* Write the buffer out using a custom routine.
*
* @param out the output stream
* @throws IOException
*/
private void writeObject(ObjectOutputStream out) throws IOException {
out.defaultWriteObject();
out.writeInt(size());
for (Iterator it = iterator(); it.hasNext();) {
out.writeObject(it.next());
}
}
/**
* Read the buffer in using a custom routine.
*
* @param in the input stream
* @throws IOException
* @throws ClassNotFoundException
*/
private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
in.defaultReadObject();
elements = new Object[maxElements];
int size = in.readInt();
for (int i = 0; i < size; i++) {
elements[i] = in.readObject();
}
start = 0;
full = (size == maxElements);
if (full) {
end = 0;
} else {
end = size;
}
}
//-----------------------------------------------------------------------
/**
* 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;
}
int pos = lastReturnedIndex + 1;
if (start < lastReturnedIndex && pos < end) {
// shift in one part
System.arraycopy(elements, pos, elements,
lastReturnedIndex, end - pos);
} else {
// Other elements require us to shift the subsequent elements
while (pos != end) {
if (pos >= maxElements) {
elements[pos - 1] = elements[0];
pos = 0;
} else {
elements[decrement(pos)] = elements[pos];
pos = increment(pos);
}
}
}
lastReturnedIndex = -1;
end = decrement(end);
elements[end] = null;
full = false;
index = decrement(index);
}
};
}
}