org.apache.lucene.util

## Class SentinelIntSet

- java.lang.Object
- - org.apache.lucene.util.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 and 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 and Description
    `SentinelIntSet(int size, int emptyVal)`

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and 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.

    - ### Methods inherited from class java.lang.Object

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

- - ### 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.

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