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* Licensed to the Apache Software Foundation (ASF) under one *
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* 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 *
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* *
* Unless required by applicable law or agreed to in writing, *
* software distributed under the License is distributed on an *
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* specific language governing permissions and limitations *
* under the License. *
****************************************************************/
package org.apache.james.mime4j.decoder;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* UnboundedFifoByteBuffer 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.
* <p>
* The removal order of an <code>UnboundedFifoByteBuffer</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 #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.
* <p>
* Note that this implementation is not synchronized. The following can be
* used to provide synchronized access to your <code>UnboundedFifoByteBuffer</code>:
* <pre>
* Buffer fifo = BufferUtils.synchronizedBuffer(new UnboundedFifoByteBuffer());
* </pre>
* <p>
* This buffer prevents null objects from being added.
*
* @since Commons Collections 3.0 (previously in main package v2.1)
* @version $Revision: 1.1 $ $Date: 2004/08/24 06:52:02 $
*
*
*
*
*
*
*/
class UnboundedFifoByteBuffer {
protected byte[] buffer;
protected int head;
protected int tail;
/**
* Constructs an UnboundedFifoByteBuffer with the default number of elements.
* It is exactly the same as performing the following:
*
* <pre>
* new UnboundedFifoByteBuffer(32);
* </pre>
*/
public UnboundedFifoByteBuffer() {
this(32);
}
/**
* Constructs an UnboundedFifoByteBuffer 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 UnboundedFifoByteBuffer(int initialSize) {
if (initialSize <= 0) {
throw new IllegalArgumentException("The size must be greater than 0");
}
buffer = new byte[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 b the byte to add
* @return true, always
*/
public boolean add(final byte b) {
if (size() + 1 >= buffer.length) {
byte[] tmp = new byte[((buffer.length - 1) * 2) + 1];
int j = 0;
for (int i = head; i != tail;) {
tmp[j] = buffer[i];
buffer[i] = 0;
j++;
i++;
if (i == buffer.length) {
i = 0;
}
}
buffer = tmp;
head = 0;
tail = j;
}
buffer[tail] = b;
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 byte get() {
if (isEmpty()) {
throw new IllegalStateException("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 byte remove() {
if (isEmpty()) {
throw new IllegalStateException("The buffer is already empty");
}
byte element = buffer[head];
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 new Byte(buffer[lastReturnedIndex]);
}
public void remove() {
if (lastReturnedIndex == -1) {
throw new IllegalStateException();
}
// First element can be removed quickly
if (lastReturnedIndex == head) {
UnboundedFifoByteBuffer.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] = 0;
index = decrement(index);
}
};
}
} |
