Package org.apache.lucene.util

Class PriorityQueue<T>

java.lang.Object

org.apache.lucene.util.PriorityQueue<T>

Direct Known Subclasses:

FieldValueHitQueue, Lookup.LookupPriorityQueue, SuggestWordQueue, TopOrdAndFloatQueue, TopOrdAndIntQueue

public abstract class PriorityQueue<T>
extends java.lang.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.

NOTE: This class will pre-allocate a full array of length maxSize+1 if instantiated via the PriorityQueue(int,boolean) constructor with prepopulate set to true.

Constructor Summary

Constructors

Constructor	Description
PriorityQueue(int maxSize)
PriorityQueue(int maxSize, boolean prepopulate)

Method Summary

Modifier and Type	Method	Description
T	add(T element)	Adds an Object to a PriorityQueue in log(size) time.
void	clear()	Removes all entries from the PriorityQueue.
T	insertWithOverflow(T element)	Adds an Object to a PriorityQueue in log(size) time.
T	pop()	Removes and returns the least element of the PriorityQueue in log(size) time.
int	size()	Returns the number of elements currently stored in the PriorityQueue.
T	top()	Returns the least element of the PriorityQueue in constant time.
T	updateTop()	Should be called when the Object at top changes values.

Methods inherited from class java.lang.Object

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

Constructor Detail

PriorityQueue

public PriorityQueue(int maxSize)

PriorityQueue

public PriorityQueue(int maxSize,
                     boolean prepopulate)

Method Detail

add

public final T add(T element)

Adds an Object to a PriorityQueue in log(size) time. If one tries to add more objects than maxSize from initialize an ArrayIndexOutOfBoundsException is thrown.

Returns:

the new 'top' element in the queue.

insertWithOverflow

public T insertWithOverflow(T element)

Adds an Object to a PriorityQueue in log(size) time. It returns the object (if any) that was dropped off the heap because it was full. This can be the given parameter (in case it is smaller than the full heap's minimum, and couldn't be added), or another object that was previously the smallest value in the heap and now has been replaced by a larger one, or null if the queue wasn't yet full with maxSize elements.

top

public final T top()

Returns the least element of the PriorityQueue in constant time.

pop

public final T pop()

Removes and returns the least element of the PriorityQueue in log(size) time.

updateTop

public final T updateTop()

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.updateTop();
 

instead of

 o = pq.pop();
 o.change();
 pq.push(o);
 

Returns:

the new 'top' element.

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.