org.apache.commons.collections.buffer

Class PriorityBuffer

public class PriorityBuffer extends AbstractCollection implements Buffer, Serializable

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 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 synchronizedBuffer or decorate to provide synchronized access to a PriorityBuffer:

 Buffer heap = SynchronizedBuffer.decorate(new PriorityBuffer());
 

This class is Serializable from Commons Collections 3.2.

Since: Commons Collections 3.0 (previously BinaryHeap v1.0)

Version: $Revision: 405927 $ $Date: 2006-05-12 23:57:03 +0100 (Fri, 12 May 2006) $

Author: Peter Donald Ram Chidambaram Michael A. Smith Paul Jack Stephen Colebourne Steve Phelps

Field Summary
protected booleanascendingOrder
If true, the first element as determined by the sort order will be returned.
protected Comparatorcomparator
The comparator used to order the elements
protected Object[]elements
The elements in this buffer.
protected intsize
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
booleanadd(Object element)
Adds an element to the buffer.
voidclear()
Clears all elements from the buffer.
Comparatorcomparator()
Gets the comparator being used for this buffer, null is natural order.
protected intcompare(Object a, Object b)
Compares two objects using the comparator if specified, or the natural order otherwise.
Objectget()
Gets the next element to be removed without actually removing it (peek).
protected voidgrow()
Increases the size of the heap to support additional elements
booleanisAscendingOrder()
Checks whether the heap is ascending or descending order.
protected booleanisAtCapacity()
Tests if the buffer is at capacity.
Iteratoriterator()
Returns an iterator over this heap's elements.
protected voidpercolateDownMaxHeap(int index)
Percolates element down heap from the position given by the index.
protected voidpercolateDownMinHeap(int index)
Percolates element down heap from the position given by the index.
protected voidpercolateUpMaxHeap(int index)
Percolates element up heap from from the position given by the index.
protected voidpercolateUpMaxHeap(Object element)
Percolates a new element up heap from the bottom.
protected voidpercolateUpMinHeap(int index)
Percolates element up heap from the position given by the index.
protected voidpercolateUpMinHeap(Object element)
Percolates a new element up heap from the bottom.
Objectremove()
Gets and removes the next element (pop).
intsize()
Returns the number of elements in this buffer.
StringtoString()
Returns a string representation of this heap.

Field Detail

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 Detail

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

Throws: IllegalArgumentException if capacity is <= 0

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

Throws: IllegalArgumentException if capacity is <= 0

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.

Throws: IllegalArgumentException if capacity is <= 0

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

Throws: IllegalArgumentException if capacity is <= 0

Method Detail

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).

Returns: the next element

Throws: BufferUnderflowException if the buffer is empty

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(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

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

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

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

remove

public Object remove()
Gets and removes the next element (pop).

Returns: the next element

Throws: BufferUnderflowException if the buffer is empty

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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