org.apache.commons.collections

Class BinaryHeap

Implemented Interfaces:
Buffer, Collection, PriorityQueue

public final class BinaryHeap
extends AbstractCollection
implements PriorityQueue, Buffer

Binary heap implementation of PriorityQueue.

The PriorityQueue interface has now been replaced for most uses by the Buffer interface. This class and the interface are retained for backwards compatibility. The intended replacement is PriorityBuffer.

The removal order of a binary heap is based on either the natural sort order of its elements or a specified Comparator. The pop() method always returns the first element as determined by the sort order. (The isMinHeap flag in the constructors can be used to reverse the sort order, in which case pop() 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 insert(Object) and pop() operations perform in logarithmic time. The peek() operation performs in constant time. All other operations perform in linear time or worse.

Note that this implementation is not synchronized. Use SynchronizedPriorityQueue to provide synchronized access to a BinaryHeap:

 PriorityQueue heap = new SynchronizedPriorityQueue(new BinaryHeap());
 
Version:
$Revision: 1.24 $ $Date: 2004/02/18 01:15:42 $
Authors:
Peter Donald
Ram Chidambaram
Michael A. Smith
Paul Jack
Stephen Colebourne
Since:
Commons Collections 1.0

Constructor Summary

BinaryHeap()
Constructs a new minimum binary heap.
BinaryHeap(Comparator comparator)
Constructs a new BinaryHeap that will use the given comparator to order its elements.
BinaryHeap(boolean isMinHeap)
Constructs a new minimum or maximum binary heap
BinaryHeap(boolean isMinHeap, Comparator comparator)
Constructs a new BinaryHeap.
BinaryHeap(int capacity)
Constructs a new minimum binary heap with the specified initial capacity.
BinaryHeap(int capacity, Comparator comparator)
Constructs a new BinaryHeap.
BinaryHeap(int capacity, boolean isMinHeap)
Constructs a new minimum or maximum binary heap with the specified initial capacity.
BinaryHeap(int capacity, boolean isMinHeap, Comparator comparator)
Constructs a new BinaryHeap.

Method Summary

boolean
add(Object object)
Adds an object to this heap.
void
clear()
Clears all elements from queue.
Object
get()
Returns the priority element.
protected void
grow()
Increases the size of the heap to support additional elements
void
insert(Object element)
Inserts an element into queue.
boolean
isEmpty()
Tests if queue is empty.
boolean
isFull()
Tests if queue is full.
Iterator
iterator()
Returns an iterator over this heap's elements.
Object
peek()
Returns the element on top of heap but don't remove it.
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
pop()
Returns the element on top of heap and remove it.
Object
remove()
Removes the priority element.
int
size()
Returns the number of elements in this heap.
String
toString()
Returns a string representation of this heap.

Constructor Details

BinaryHeap

public BinaryHeap()
Constructs a new minimum binary heap.

BinaryHeap

public BinaryHeap(Comparator comparator)
Constructs a new BinaryHeap that will use the given comparator to order its elements.
Parameters:
comparator - the comparator used to order the elements, null means use natural order

BinaryHeap

public BinaryHeap(boolean isMinHeap)
Constructs a new minimum or maximum binary heap
Parameters:
isMinHeap - if true the heap is created as a minimum heap; otherwise, the heap is created as a maximum heap

BinaryHeap

public BinaryHeap(boolean isMinHeap,
                  Comparator comparator)
Constructs a new BinaryHeap.
Parameters:
isMinHeap - 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

BinaryHeap

public BinaryHeap(int capacity)
Constructs a new minimum binary heap with the specified initial capacity.
Parameters:
capacity - The initial capacity for the heap. This value must be greater than zero.

BinaryHeap

public BinaryHeap(int capacity,
                  Comparator comparator)
Constructs a new BinaryHeap.
Parameters:
capacity - the initial capacity for the heap
comparator - the comparator used to order the elements, null means use natural order

BinaryHeap

public BinaryHeap(int capacity,
                  boolean isMinHeap)
Constructs a new minimum or maximum binary heap with the specified initial capacity.
Parameters:
capacity - the initial capacity for the heap. This value must be greater than zero.
isMinHeap - if true the heap is created as a minimum heap; otherwise, the heap is created as a maximum heap.

BinaryHeap

public BinaryHeap(int capacity,
                  boolean isMinHeap,
                  Comparator comparator)
Constructs a new BinaryHeap.
Parameters:
capacity - the initial capacity for the heap
isMinHeap - 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 object)
Parameters:
object - the object to add
Returns:
true, always

clear

public void clear()
Clears all elements from queue.
Specified by:
clear in interface PriorityQueue

get

public Object get()
Specified by:
get in interface Buffer
Returns:
the priority element

grow

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

insert

public void insert(Object element)
Inserts an element into queue.
Specified by:
insert in interface PriorityQueue
Parameters:
element - the element to be inserted

isEmpty

public boolean isEmpty()
Tests if queue is empty.
Specified by:
isEmpty in interface PriorityQueue
Returns:
true if queue is empty; false otherwise.

isFull

public boolean isFull()
Tests if queue is full.
Returns:
true if queue is full; false otherwise.

iterator

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

peek

public Object peek()
            throws NoSuchElementException
Returns the element on top of heap but don't remove it.
Specified by:
peek in interface PriorityQueue
Returns:
the element at top of heap

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

pop

public Object pop()
            throws NoSuchElementException
Returns the element on top of heap and remove it.
Specified by:
pop in interface PriorityQueue
Returns:
the element at top of heap

remove

public Object remove()
Specified by:
remove in interface Buffer
Returns:
the removed priority element

size

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

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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