org.apache.lucene.util
Class PriorityQueue

Object
  extended by PriorityQueue
Direct Known Subclasses:
HitQueue, MoreLikeThisQuery.QueryWordQueue, SpanOrQuery.SpanQueue, SpellReader.WordQueue

public abstract class PriorityQueue
extends Object

A PriorityQueue maintains a partial ordering of its elements such that the least element can always be found in constant time. Put()'s and pop()'s require log(size) time.


Field Summary
private  boolean expandable
           
private  Object[] heap
           
private  int maxSize
           
private  int size
           
 
Constructor Summary
PriorityQueue()
           
 
Method Summary
 void adjustTop()
          Should be called when the Object at top changes values.
 void clear()
          Removes all entries from the PriorityQueue.
private  void downHeap()
           
private  void expand()
          Make the queue bigger.
protected  void initialize(int maxSize)
          Subclass constructors must call this.
 boolean insert(Object element)
          Adds element to the PriorityQueue in log(size) time if either the PriorityQueue is not full, or not lessThan(element, top()).
protected abstract  boolean lessThan(Object a, Object b)
          Determines the ordering of objects in this priority queue.
 Object pop()
          Removes and returns the least element of the PriorityQueue in log(size) time.
 void put(Object element)
          Adds an Object to a PriorityQueue in log(size) time.
 void setExpandable()
          Make the queue expandable (will resize if full)
 int size()
          Returns the number of elements currently stored in the PriorityQueue.
 Object top()
          Returns the least element of the PriorityQueue in constant time.
private  void upHeap()
           
 
Methods inherited from class Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

heap

private Object[] heap

size

private int size

maxSize

private int maxSize

expandable

private boolean expandable
Constructor Detail

PriorityQueue

public PriorityQueue()
Method Detail

lessThan

protected abstract boolean lessThan(Object a,
                                    Object b)
Determines the ordering of objects in this priority queue. Subclasses must define this one method.


initialize

protected final void initialize(int maxSize)
Subclass constructors must call this.


setExpandable

public void setExpandable()
Make the queue expandable (will resize if full)


expand

private void expand()
Make the queue bigger.


put

public final void put(Object element)
Adds an Object to a PriorityQueue in log(size) time. If one tries to add more objects than maxSize from initialize a RuntimeException (ArrayIndexOutOfBound) is thrown.


insert

public boolean insert(Object element)
Adds element to the PriorityQueue in log(size) time if either the PriorityQueue is not full, or not lessThan(element, top()).

Parameters:
element -
Returns:
true if element is added, false otherwise.

top

public final Object top()
Returns the least element of the PriorityQueue in constant time.


pop

public final Object pop()
Removes and returns the least element of the PriorityQueue in log(size) time.


adjustTop

public final void adjustTop()
Should be called when the Object at top changes values. Still log(n) worst case, but it's at least twice as fast to
  { pq.top().change(); pq.adjustTop(); }
 
instead of
  { o = pq.pop(); o.change(); pq.push(o); }
 


size

public final int size()
Returns the number of elements currently stored in the PriorityQueue.


clear

public final void clear()
Removes all entries from the PriorityQueue.


upHeap

private final void upHeap()

downHeap

private final void downHeap()