org.apache.lucene.util
Class PriorityQueue

java.lang.Object
  |
  +--org.apache.lucene.util.PriorityQueue

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.

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.
protected void	initialize(int maxSize) Subclass constructors must call this.
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.
int	size() Returns the number of elements currently stored in the PriorityQueue.
Object	top() Returns the least element of the PriorityQueue in constant time.

Methods inherited from class java.lang.Object

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

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.

put

public final void put(Object element)

Adds an Object to a PriorityQueue in log(size) time.

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.