Package org.apache.lucene.util

Class SentinelIntSet

  • public class SentinelIntSet
extends Object
    A native int hash-based set where one value is reserved to mean "EMPTY" internally. The space overhead is fairly low as there is only one power-of-two sized int[] to hold the values. The set is re-hashed when adding a value that would make it >= 75% full. Consider extending and over-riding hash(int) if the values might be poor hash keys; Lucene docids should be fine. The internal fields are exposed publicly to enable more efficient use at the expense of better O-O principles.

    To iterate over the integers held in this set, simply use code like this: 

     SentinelIntSet set = ...
 for (int v : set.keys) {
   if (v == set.emptyVal)
     continue;
   //use v...
 }

    • Field Summary

      Fields 
      Modifier and Type Field Description
      int count  
      int emptyVal  
      int[] keys
      A power-of-2 over-sized array holding the integers in the set along with empty values.
      int rehashCount
      the count at which a rehash should be done

    • Constructor Summary

      Constructors 
      Constructor Description
      SentinelIntSet​(int size, int emptyVal)  

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void clear()  
      boolean exists​(int key)
      Does this set contain the specified integer?
      int find​(int key)
      (internal) Returns the slot for this key, or -slot-1 if not found
      int getSlot​(int key)
      (internal) Returns the slot for this key
      int hash​(int key)
      (internal) Return the hash for the key.
      int put​(int key)
      Puts this integer (key) in the set, and returns the slot index it was added to.
      void rehash()
      (internal) Rehashes by doubling int[] key and filling with the old values.
      int size()
      The number of integers in this set.

    • Field Detail

      • keys

        public int[] keys
        A power-of-2 over-sized array holding the integers in the set along with empty values.

      • count

        public int count

      • emptyVal

        public final int emptyVal

      • rehashCount

        public int rehashCount
        the count at which a rehash should be done

    • Constructor Detail

      • SentinelIntSet

        public SentinelIntSet​(int size,
                      int emptyVal)
        Parameters:
        size - The minimum number of elements this set should be able to hold without rehashing (i.e. the slots are guaranteed not to change)
        emptyVal - The integer value to use for EMPTY

    • Method Detail

      • clear

        public void clear()

      • hash

        public int hash​(int key)
        (internal) Return the hash for the key. The default implementation just returns the key, which is not appropriate for general purpose use.

      • size

        public int size()
        The number of integers in this set.

      • getSlot

        public int getSlot​(int key)
        (internal) Returns the slot for this key

      • find

        public int find​(int key)
        (internal) Returns the slot for this key, or -slot-1 if not found

      • exists

        public boolean exists​(int key)
        Does this set contain the specified integer?

      • put

        public int put​(int key)
        Puts this integer (key) in the set, and returns the slot index it was added to. It rehashes if adding it would make the set more than 75% full.

      • rehash

        public void rehash()
        (internal) Rehashes by doubling int[] key and filling with the old values.