PriorityBuffer (Apache Commons Collections 3.2.2 API)

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

All Implemented Interfaces:

Serializable, Iterable, Collection, Buffer
```
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(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());
 
```
This class is Serializable from Commons Collections 3.2.
Since:

Commons Collections 3.0 (previously BinaryHeap v1.0)

Version:

$Revision: 972404 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $

Author:

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

See Also:
Serialized Form

Field Summary

Fields
Modifier and Type	Field and Description
`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

Constructors
Constructor and Description
`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, Comparator comparator)` Constructs a new empty buffer specifying the sort order and comparator.
`PriorityBuffer(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, Comparator comparator)` Constructs a new empty buffer that specifying initial capacity, sort order and comparator.
`PriorityBuffer(int capacity, Comparator comparator)` Constructs a new empty buffer that sorts in ascending order using the specified comparator and initial capacity.

Method Summary

Methods
Modifier and Type	Method and Description
`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(int index)` Percolates element up heap from from the position given by the index.
`protected void`	`percolateUpMaxHeap(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.
`protected void`	`percolateUpMinHeap(Object element)` Percolates a new element up heap from the bottom.
`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.

Methods inherited from class java.util.AbstractCollection
addAll, contains, containsAll, isEmpty, remove, removeAll, retainAll, toArray, toArray

Methods inherited from class java.lang.Object
clone, equals, finalize, 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

- Field Detail
  - elements
```
protected Object[] elements
```
    The elements in this buffer.
  - size
```
protected int size
```
    The number of elements currently in this buffer.
  - 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
- 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
  - isAscendingOrder
```
public boolean isAscendingOrder()
```
    Checks whether the heap is ascending or descending order.
    
    Returns:
    true if ascending order (a min heap)
  - 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
  - size
```
public int size()
```
    Returns the number of elements in this buffer.
    
    Specified by:
    
    size in interface Collection
    
    Specified by:
    
    size in class AbstractCollection
    
    Returns:
    the number of elements in this buffer
  - clear
```
public void clear()
```
    Clears all elements from the buffer.
    
    Specified by:
    
    clear in interface Collection
    
    Overrides:
    
    clear in class AbstractCollection
  - add
```
public boolean add(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 Collection
    
    Overrides:
    
    add in class AbstractCollection
    
    Parameters:
    element - the element to be added
    
    Returns:
    true always
  - 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
    
    Throws:
    
    BufferUnderflowException - if the buffer is empty
  - remove
```
public 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
  - isAtCapacity
```
protected boolean isAtCapacity()
```
    Tests if the buffer is at capacity.
    
    Returns:
    true if buffer is full; false otherwise.
  - 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
  - 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
  - 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
  - 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
  - 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
  - grow
```
protected void grow()
```
    Increases the size of the heap to support additional elements
  - iterator
```
public Iterator iterator()
```
    Returns an iterator over this heap's elements.
    
    Specified by:
    
    iterator in interface Iterable
    
    Specified by:
    
    iterator in interface Collection
    
    Specified by:
    
    iterator in class AbstractCollection
    
    Returns:
    an iterator over this heap's elements
  - toString
```
public 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 AbstractCollection
    
    Returns:
    a string representation of this heap

Class PriorityBuffer

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.util.AbstractCollection

Methods inherited from class java.lang.Object

Methods inherited from interface java.util.Collection

Field Detail

elements

size

ascendingOrder

comparator

Constructor Detail

PriorityBuffer

PriorityBuffer

PriorityBuffer

PriorityBuffer

PriorityBuffer

PriorityBuffer

PriorityBuffer

PriorityBuffer

Method Detail

isAscendingOrder

comparator

size

clear

add

get

remove

isAtCapacity

percolateDownMinHeap

percolateDownMaxHeap

percolateUpMinHeap

percolateUpMinHeap

percolateUpMaxHeap

percolateUpMaxHeap

compare

grow

iterator

toString