org.apache.hadoop.util
Class PriorityQueue<T>

java.lang.Object
  extended by org.apache.hadoop.util.PriorityQueue<T>

public abstract class PriorityQueue<T>
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.
 boolean insert(T 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.
 T pop()
          Removes and returns the least element of the PriorityQueue in log(size) time.
 void put(T element)
          Adds an Object to a 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.
 
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(T 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(T 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 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.


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.



Copyright © 2009 The Apache Software Foundation