Package 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
Description
`int`
`count`
`final 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

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.

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

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

## Field Details

### 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 Details

### 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 Details

### 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.