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...
 }
    NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.

    • 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.
      long ramBytesUsed()
      Return the memory footprint of this class in bytes.
      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.

      • ramBytesUsed

        public long ramBytesUsed()
        Return the memory footprint of this class in bytes.