org.apache.commons.collections.buffer

Class PriorityBuffer

Implemented Interfaces:
Buffer, Collection

public class PriorityBuffer
extends AbstractCollection
implements Buffer

Binary heap implementation of Buffer that provides for removal based on Comparator ordering.

The removal order of a binary heap is based on either the natural sort order of its elements or a specified Comparator. The remove() method always returns the first element as determined by the sort order. (The ascendingOrder flag in the constructors can be used to reverse the sort order, in which case remove() will always remove the last element.) The removal order is not the same as the order of iteration; elements are returned by the iterator in no particular order.

The add(Object) and remove() operations perform in logarithmic time. The get() operation performs in constant time. All other operations perform in linear time or worse.

Note that this implementation is not synchronized. Use BufferUtils.synchronizedBuffer(Buffer) or SynchronizedBuffer.decorate(Buffer) to provide synchronized access to a PriorityBuffer:

 Buffer heap = SynchronizedBuffer.decorate(new PriorityBuffer());
 
Version:
$Revision: 1.5 $ $Date: 2004/05/15 12:33:23 $
Authors:
Peter Donald
Ram Chidambaram
Michael A. Smith
Paul Jack
Stephen Colebourne
Since:
Commons Collections 3.0 (previously BinaryHeap v1.0)

Field Summary

protected boolean
ascendingOrder
If true, the first element as determined by the sort order will be returned.
protected Comparator
comparator
The comparator used to order the elements
protected Object[]
elements
The elements in this buffer.
protected int
size
The number of elements currently in this buffer.

Constructor Summary

PriorityBuffer()
Constructs a new empty buffer that sorts in ascending order by the natural order of the objects added.
PriorityBuffer(Comparator comparator)
Constructs a new empty buffer that sorts in ascending order using the specified comparator.
PriorityBuffer(boolean ascendingOrder)
Constructs a new empty buffer specifying the sort order and using the natural order of the objects added.
PriorityBuffer(boolean ascendingOrder, Comparator comparator)
Constructs a new empty buffer specifying the sort order and comparator.
PriorityBuffer(int capacity)
Constructs a new empty buffer that sorts in ascending order by the natural order of the objects added, specifying an initial capacity.
PriorityBuffer(int capacity, Comparator comparator)
Constructs a new empty buffer that sorts in ascending order using the specified comparator and initial capacity.
PriorityBuffer(int capacity, boolean ascendingOrder)
Constructs a new empty buffer that specifying initial capacity and sort order, using the natural order of the objects added.
PriorityBuffer(int capacity, boolean ascendingOrder, Comparator comparator)
Constructs a new empty buffer that specifying initial capacity, sort order and comparator.

Method Summary

boolean
add(Object element)
Adds an element to the buffer.
void
clear()
Clears all elements from the buffer.
Comparator
comparator()
Gets the comparator being used for this buffer, null is natural order.
protected int
compare(Object a, Object b)
Compares two objects using the comparator if specified, or the natural order otherwise.
Object
get()
Gets the next element to be removed without actually removing it (peek).
protected void
grow()
Increases the size of the heap to support additional elements
boolean
isAscendingOrder()
Checks whether the heap is ascending or descending order.
protected boolean
isAtCapacity()
Tests if the buffer is at capacity.
Iterator
iterator()
Returns an iterator over this heap's elements.
protected void
percolateDownMaxHeap(int index)
Percolates element down heap from the position given by the index.
protected void
percolateDownMinHeap(int index)
Percolates element down heap from the position given by the index.
protected void
percolateUpMaxHeap(Object element)
Percolates a new element up heap from the bottom.
protected void
percolateUpMaxHeap(int index)
Percolates element up heap from from the position given by the index.
protected void
percolateUpMinHeap(Object element)
Percolates a new element up heap from the bottom.
protected void
percolateUpMinHeap(int index)
Percolates element up heap from the position given by the index.
Object
remove()
Gets and removes the next element (pop).
int
size()
Returns the number of elements in this buffer.
String
toString()
Returns a string representation of this heap.

Field Details

ascendingOrder

protected boolean ascendingOrder
If true, the first element as determined by the sort order will be returned. If false, the last element as determined by the sort order will be returned.

comparator

protected Comparator comparator
The comparator used to order the elements

elements

protected Object[] elements
The elements in this buffer.

size

protected int size
The number of elements currently in this buffer.

Constructor Details

PriorityBuffer

public PriorityBuffer()
Constructs a new empty buffer that sorts in ascending order by the natural order of the objects added.

PriorityBuffer

public PriorityBuffer(Comparator comparator)
Constructs a new empty buffer that sorts in ascending order using the specified comparator.
Parameters:
comparator - the comparator used to order the elements, null means use natural order

PriorityBuffer

public PriorityBuffer(boolean ascendingOrder)
Constructs a new empty buffer specifying the sort order and using the natural order of the objects added.
Parameters:
ascendingOrder - if true the heap is created as a minimum heap; otherwise, the heap is created as a maximum heap

PriorityBuffer

public PriorityBuffer(boolean ascendingOrder,
                      Comparator comparator)
Constructs a new empty buffer specifying the sort order and comparator.
Parameters:
ascendingOrder - true to use the order imposed by the given comparator; false to reverse that order
comparator - the comparator used to order the elements, null means use natural order

PriorityBuffer

public PriorityBuffer(int capacity)
Constructs a new empty buffer that sorts in ascending order by the natural order of the objects added, specifying an initial capacity.
Parameters:
capacity - the initial capacity for the buffer, greater than zero

PriorityBuffer

public PriorityBuffer(int capacity,
                      Comparator comparator)
Constructs a new empty buffer that sorts in ascending order using the specified comparator and initial capacity.
Parameters:
capacity - the initial capacity for the buffer, greater than zero
comparator - the comparator used to order the elements, null means use natural order

PriorityBuffer

public PriorityBuffer(int capacity,
                      boolean ascendingOrder)
Constructs a new empty buffer that specifying initial capacity and sort order, using the natural order of the objects added.
Parameters:
capacity - the initial capacity for the buffer, greater than zero
ascendingOrder - if true the heap is created as a minimum heap; otherwise, the heap is created as a maximum heap.

PriorityBuffer

public PriorityBuffer(int capacity,
                      boolean ascendingOrder,
                      Comparator comparator)
Constructs a new empty buffer that specifying initial capacity, sort order and comparator.
Parameters:
capacity - the initial capacity for the buffer, greater than zero
ascendingOrder - true to use the order imposed by the given comparator; false to reverse that order
comparator - the comparator used to order the elements, null means use natural order

Method Details

add

public boolean add(Object element)
Adds an element to the buffer.

The element added will be sorted according to the comparator in use.

Parameters:
element - the element to be added
Returns:
true always

clear

public void clear()
Clears all elements from the buffer.

comparator

public Comparator comparator()
Gets the comparator being used for this buffer, null is natural order.
Returns:
the comparator in use, null is natural order

compare

protected int compare(Object a,
                      Object b)
Compares two objects using the comparator if specified, or the natural order otherwise.
Parameters:
a - the first object
b - the second object
Returns:
-ve if a less than b, 0 if they are equal, +ve if a greater than b

get

public Object get()
Gets the next element to be removed without actually removing it (peek).
Specified by:
get in interface Buffer
Returns:
the next element

grow

protected void grow()
Increases the size of the heap to support additional elements

isAscendingOrder

public boolean isAscendingOrder()
Checks whether the heap is ascending or descending order.
Returns:
true if ascending order (a min heap)

isAtCapacity

protected boolean isAtCapacity()
Tests if the buffer is at capacity.
Returns:
true if buffer is full; false otherwise.

iterator

public Iterator iterator()
Returns an iterator over this heap's elements.
Returns:
an iterator over this heap's elements

percolateDownMaxHeap

protected void percolateDownMaxHeap(int index)
Percolates element down heap from the position given by the index.

Assumes it is a maximum heap.

Parameters:
index - the index of the element

percolateDownMinHeap

protected void percolateDownMinHeap(int index)
Percolates element down heap from the position given by the index.

Assumes it is a minimum heap.

Parameters:
index - the index for the element

percolateUpMaxHeap

protected void percolateUpMaxHeap(Object element)
Percolates a new element up heap from the bottom.

Assume it is a maximum heap.

Parameters:
element - the element

percolateUpMaxHeap

protected void percolateUpMaxHeap(int index)
Percolates element up heap from from the position given by the index.

Assume it is a maximum heap.

Parameters:
index - the index of the element to be percolated up

percolateUpMinHeap

protected void percolateUpMinHeap(Object element)
Percolates a new element up heap from the bottom.

Assumes it is a minimum heap.

Parameters:
element - the element

percolateUpMinHeap

protected void percolateUpMinHeap(int index)
Percolates element up heap from the position given by the index.

Assumes it is a minimum heap.

Parameters:
index - the index of the element to be percolated up

remove

public Object remove()
Gets and removes the next element (pop).
Specified by:
remove in interface Buffer
Returns:
the next element

size

public int size()
Returns the number of elements in this buffer.
Returns:
the number of elements in this buffer

toString

public String toString()
Returns a string representation of this heap. The returned string is similar to those produced by standard JDK collections.
Returns:
a string representation of this heap

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