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/*
* File: FiniteCapacityBuffer.java
* Authors: Kevin R. Dixon
* Company: Sandia National Laboratories
* Project: Cognitive Foundry
*
* Copyright July 24, 2007, Sandia Corporation. Under the terms of Contract
* DE-AC04-94AL85000, there is a non-exclusive license for use of this work by
* or on behalf of the U.S. Government. Export of this program may require a
* license from the United States Government. See CopyrightHistory.txt for
* complete details.
*
*/
package gov.sandia.cognition.collection;
import gov.sandia.cognition.annotation.CodeReview;
import gov.sandia.cognition.util.ArgumentChecker;
import gov.sandia.cognition.util.CloneableSerializable;
import gov.sandia.cognition.util.ObjectUtil;
import java.util.AbstractList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.ListIterator;
/**
* A finite capacity buffer backed by a fixed array. One can add and remove
* from the buffer, but the size will never be greater than the capacity.
* The running times are constant, except for removing in the middle
* of the list, which may require a relatively expensive copy/shift.
* This is essentially a circular array-back list.
*
* @param Type of data contained in the buffer
* @author Kevin R. Dixon
* @since 2.0
*
*/
@CodeReview(
reviewer="Kevin R. Dixon",
date="2008-02-08",
changesNeeded=false,
comments={
"Cleaned up minor formatting issues.",
"Added class documentation about running times and usage of LinkedList."
}
)
public class FiniteCapacityBuffer
extends AbstractList
implements CloneableSerializable
{
/**
* Underlying data in the buffer
*/
private Object[] data;
/**
* Location of element 0
*/
private int head;
/**
* Number of items in the list
*/
private int size;
/**
* Default constructor with capacity of one.
*/
public FiniteCapacityBuffer()
{
this(1);
}
/**
* Creates a new instance of FiniteCapacityBuffer.
*
* @param capacity
* Maximum capacity of the buffer.
*/
@SuppressWarnings("unchecked")
public FiniteCapacityBuffer(
int capacity)
{
this.data = new Object[ 0 ];
this.head = 0;
this.setCapacity(capacity);
}
/**
* Copy constructor.
*
* @param other
* FiniteCapacityBuffer to copy.
*/
public FiniteCapacityBuffer(
FiniteCapacityBuffer other)
{
this(other.getCapacity());
this.addAll(other);
}
@Override
public FiniteCapacityBuffer clone()
{
try
{
@SuppressWarnings(value = "unchecked")
FiniteCapacityBuffer clone =
(FiniteCapacityBuffer) super.clone();
clone.data = ObjectUtil.cloneSmartArrayAndElements(this.data);
return clone;
}
catch (CloneNotSupportedException ex)
{
throw new RuntimeException(ex);
}
}
@Override
public int size()
{
return this.size;
}
@Override
public Iterator iterator()
{
return new InternalIterator();
}
/**
* Appends the element to the end of the buffer, removing excess elements
* if necessary
* @param e
* DataType to addLast to the buffer
* @return true if successful, false if unable to add
*/
@Override
public boolean add(
DataType e)
{
return this.addLast(e);
}
@Override
public boolean remove(
Object o)
{
DataType retval = null;
for( int i = 0; i < this.size; i++ )
{
Object vi = this.get(i);
if( vi.equals(o) )
{
retval = this.remove(i);
break;
}
}
return retval != null;
}
@Override
public DataType remove(
final int index)
{
ArgumentChecker.assertIsInRangeInclusive("index", index, 0, this.size-1);
final int pos = this.convert(index);
@SuppressWarnings("unchecked")
DataType retval = (DataType) this.data[pos];
this.data[pos] = null;
// We just removed the first thing in the list, so just
// move the head forward
if( index == 0 )
{
this.head = this.convert(1);
}
// If you removed the final thing in the list, then there's nothing
// left to do
else if( index == this.size-1 )
{
}
// You removed something in the middle of the list, so we need to
// move things around
else
{
// If the list wraps around, then we need to recopy the entire thing
final int tail = this.convert(this.size-1);
// If the tail is "above" the removed element, then just copy
// from that element onward
if( pos < tail )
{
System.arraycopy( this.data, pos+1, this.data, pos, tail-pos );
}
// Uh-oh... the pos is "above" the tail, which means we're in a
// wrapped around state... this is harder.
else
{
for( int i = index; i < this.size-1; i++ )
{
this.set(i, this.get(i+1) );
}
}
}
this.size--;
return retval;
}
/**
* Converts the given index from zero-based world to circular world
* @param index
* Index to convert to circular world
* @return
* Circular world index
*/
protected int convert(
int index )
{
final int capacity = this.getCapacity();
int pos = (index+this.head) % this.getCapacity();
while( pos < 0 )
{
pos += capacity;
}
return pos;
}
@Override
public void clear()
{
Arrays.fill( this.data, null );
this.size = 0;
this.head = 0;
}
/**
* Prepend the element to the beginning of the buffer, removing excess
* elements if necessary
* @param e
* DataType to addFirst to the buffer
* @return true if successful, false if unable to add
*/
public boolean addFirst(
DataType e)
{
// Ensure we've got at least one free slot
final int capacity = this.getCapacity();
if( this.size >= capacity )
{
this.size = capacity-1;
}
// We should have at least
this.head = this.convert(-1);
this.data[this.head] = e;
this.size++;
return true;
}
/**
* Appends the element to the end of the buffer, removing excess elements
* if necessary
* @param e
* DataType to add to the buffer
* @return true if successful, false if unable to add
*/
public boolean addLast(
DataType e)
{
// Ensure we've got at least one free slot
final int capacity = this.getCapacity();
if( this.size >= capacity )
{
this.head = this.convert(1);
this.size = capacity-1;
}
final int tail = this.convert(this.size);
this.data[tail] = e;
this.size++;
return true;
}
/**
* Returns the first element in the list.
*
* @return
* The first element in the list.
*/
public DataType getFirst()
{
return this.get(0);
}
/**
* Returns the last element in the list.
*
* @return
* The last element in the list.
*/
public DataType getLast()
{
return this.get(this.size-1);
}
/**
* Returns true if the finite-capacity buffer is full. This means that
* the number of elements in the buffer is equal to the capacity of the
* buffer. Adding an element to the full buffer
*
* @return
* True if the buffer is full.
*/
public boolean isFull()
{
return this.size() >= this.getCapacity();
}
/**
* Gets the capacity of the buffer, which is the maximum number of elements
* that can be stored in it. Must be greater than zero.
*
* @return The maximum capacity of the buffer.
*/
public int getCapacity()
{
return this.data.length;
}
/**
* Sets the capacity of the buffer, which is the maximum number of elements
* that can be stored in it. Must be greater than zero.
*
* @param capacity
* The maximum capacity of the buffer. Must be greater than zero.
*/
public void setCapacity(
int capacity)
{
ArgumentChecker.assertIsPositive("capacity", capacity);
Object[] newData = new Object[ capacity ];
if( this.data != null )
{
// Copy over all the old elements if we're growing the buffer
int max = Math.min( this.size, capacity );
for( int i = 0; i < max; i++ )
{
// I'm sure there's a clever way to use System.arraycopy here,
// but it doesn't seem worth the effort
newData[i] = this.get(i);
}
this.size = max;
}
else
{
this.size = 0;
}
this.data = newData;
this.head = 0;
}
@Override
@SuppressWarnings("unchecked")
public DataType get(
int index)
{
ArgumentChecker.assertIsInRangeInclusive("index", index, 0, this.size-1);
return (DataType) this.data[this.convert(index)];
}
@Override
public DataType set(
int index,
DataType element)
{
ArgumentChecker.assertIsInRangeInclusive("index", index, 0, this.size-1);
int pos = this.convert(index);
@SuppressWarnings("unchecked")
DataType oldValue = (DataType) this.data[pos];
this.data[pos] = element;
return oldValue;
}
/**
* Iterator for FiniteCapacityBuffer
*/
protected class InternalIterator
implements ListIterator
{
/**
* Index of the last value retrieved
*/
private int index;
/**
* Default constructor
*/
public InternalIterator()
{
this.index = -1;
}
@Override
public boolean hasNext()
{
return this.index < size-1;
}
@Override
public DataType next()
{
this.index++;
return get(this.index);
}
@Override
public void remove()
{
FiniteCapacityBuffer.this.remove(this.index);
this.index--;
}
@Override
public boolean hasPrevious()
{
return (this.index > 0) && (size > 0);
}
@Override
public DataType previous()
{
return get(this.index);
}
@Override
public int nextIndex()
{
return this.index+1;
}
@Override
public int previousIndex()
{
return this.index;
}
@Override
public void set(
DataType o)
{
FiniteCapacityBuffer.this.set(this.index+1, o);
}
@Override
public void add(
DataType o)
{
FiniteCapacityBuffer.this.add(this.index, o);
}
}
}
