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 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
    final T
    add(T element)
    Adds an Object to a PriorityQueue in log(size) time.
    final void
    clear()
    Removes all entries from the PriorityQueue.
    T
    insertWithOverflow(T element)
    Adds an Object to a PriorityQueue in log(size) time.
    final T
    pop()
    Removes and returns the least element of the PriorityQueue in log(size) time.
    final int
    size()
    Returns the number of elements currently stored in the PriorityQueue.
    final T
    top()
    Returns the least element of the PriorityQueue in constant time.
    final 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 Details

    • PriorityQueue

      public PriorityQueue(int maxSize)

    • PriorityQueue

      public PriorityQueue(int maxSize, boolean prepopulate)

  • Method Details

    • 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.