org.apache.commons.collections.buffer
Class PriorityBuffer

java.lang.Object
  |
  +--java.util.AbstractCollection
        |
        +--org.apache.commons.collections.buffer.PriorityBuffer

All Implemented Interfaces:

Buffer, java.util.Collection

public class PriorityBuffer

extends java.util.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());
 

Since:

Commons Collections 3.0 (previously BinaryHeap v1.0)

Version:

$Revision: 1.5 $ $Date: 2004/05/15 12:33:23 $

Author:

Peter Donald, Ram Chidambaram, Michael A. Smith, Paul Jack, Stephen Colebourne

Constructor Summary

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

PriorityBuffer(boolean ascendingOrder)
Constructs a new empty buffer specifying the sort order and using the natural order of the objects added.

PriorityBuffer(boolean ascendingOrder, java.util.Comparator comparator)
Constructs a new empty buffer specifying the sort order and comparator.

PriorityBuffer(java.util.Comparator comparator)
Constructs a new empty buffer that sorts in ascending order using the specified 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, 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, java.util.Comparator comparator)
Constructs a new empty buffer that specifying initial capacity, sort order and comparator.

PriorityBuffer(int capacity, java.util.Comparator comparator)
Constructs a new empty buffer that sorts in ascending order using the specified comparator and initial capacity.

Method Summary

boolean	add(java.lang.Object element) Adds an element to the buffer.
void	clear() Clears all elements from the buffer.
java.util.Comparator	comparator() Gets the comparator being used for this buffer, null is natural order.
java.lang.Object	get() Gets the next element to be removed without actually removing it (peek).
boolean	isAscendingOrder() Checks whether the heap is ascending or descending order.
java.util.Iterator	iterator() Returns an iterator over this heap's elements.
java.lang.Object	remove() Gets and removes the next element (pop).
int	size() Returns the number of elements in this buffer.
java.lang.String	toString() Returns a string representation of this heap.

Methods inherited from class java.util.AbstractCollection

addAll, contains, containsAll, isEmpty, remove, removeAll, retainAll, toArray, toArray

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Collection

addAll, contains, containsAll, equals, hashCode, isEmpty, remove, removeAll, retainAll, toArray, toArray

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(java.util.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,
                      java.util.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:

java.lang.IllegalArgumentException - if capacity is <= 0

PriorityBuffer

public PriorityBuffer(int capacity,
                      java.util.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:

java.lang.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:

java.lang.IllegalArgumentException - if capacity is <= 0

PriorityBuffer

public PriorityBuffer(int capacity,
                      boolean ascendingOrder,
                      java.util.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:

java.lang.IllegalArgumentException - if capacity is <= 0

Method Detail

isAscendingOrder

public boolean isAscendingOrder()

Checks whether the heap is ascending or descending order.

Returns:

true if ascending order (a min heap)

comparator

public java.util.Comparator comparator()

Gets the comparator being used for this buffer, null is natural order.

Returns:

the comparator in use, null is natural order

size

public int size()

Returns the number of elements in this buffer.

Specified by:

size in interface java.util.Collection

Specified by:

size in class java.util.AbstractCollection

Returns:

the number of elements in this buffer

clear

public void clear()

Clears all elements from the buffer.

Specified by:

clear in interface java.util.Collection

Overrides:

clear in class java.util.AbstractCollection

add

public boolean add(java.lang.Object element)

Adds an element to the buffer.

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

Specified by:

add in interface java.util.Collection

Overrides:

add in class java.util.AbstractCollection

Parameters:

element - the element to be added

Returns:

true always

get

public java.lang.Object get()

Gets the next element to be removed without actually removing it (peek).

Specified by:

get in interface Buffer

Returns:

the next element

Throws:

BufferUnderflowException - if the buffer is empty

remove

public java.lang.Object remove()

Gets and removes the next element (pop).

Specified by:

remove in interface Buffer

Returns:

the next element

Throws:

BufferUnderflowException - if the buffer is empty

iterator

public java.util.Iterator iterator()

Returns an iterator over this heap's elements.

Specified by:

iterator in interface java.util.Collection

Specified by:

iterator in class java.util.AbstractCollection

Returns:

an iterator over this heap's elements

toString

public java.lang.String toString()

Returns a string representation of this heap. The returned string is similar to those produced by standard JDK collections.

Overrides:

toString in class java.util.AbstractCollection

Returns:

a string representation of this heap