org.forgerock.bloomfilter

Interface BloomFilter<E>

Type Parameters:

E - the type of elements contained in the bloom filter.

All Known Implementing Classes:

BloomFilterMonitor, ConcurrentRollingBloomFilter

public interface BloomFilter<E>

General interface contract for implementations of Bloom Filters. A Bloom Filter is a Set-like data structure that uses only a few bits of memory per element stored. This allows very large numbers (billions) of elements to be stored in-memory, with the trade-off being that set containment can now return false positives. That is, the Bloom Filter can say for certain if a given element is definitely not in the set, but it cannot say for certain whether it is. Bloom Filters are therefore appropriate as a quick initial check to reduce load on a more expensive but more accurate storage mechanism (e.g., a database) or where some level of false positives is tolerable. The expected usage pattern for the former case would be something like the following psuedo-code:

     BloomFilter<T> filter = ...;
     Set<T> expensiveSet = ...; // e.g. database, web-service
     if (filter.mightContain(element)) {
         // Perform the more expensive check to be sure
         return expensive.contains(element);
     }
     return false;
 

Note: this assumes that the Bloom Filter is kept in-sync with the definitive set! How this is accomplished is outside of the scope of this package.

All Bloom Filter implementations in this package allow the probability of false positives (FPP) to be specified, and the implementation will adjust the amount of memory used to ensure the given level of accuracy for the expected number of elements.

See Also:

Bloom Filter Wikipedia entry.

Method Summary

Modifier and Type	Method and Description
void	add(E element) Adds the specified element to this set if it is not already possibly present.
void	addAll(Collection<? extends E> elements) Adds all of the specified elements to this set if they are not possibly already present.
BloomFilterStatistics	getStatistics() Gets a snapshot of the current statistics of the set.
boolean	mightContain(E element) Checks if the given element might be a member of this set.

Method Detail

add

void add(E element)

Adds the specified element to this set if it is not already possibly present. After a call to this method, subsequent calls to mightContain(Object) will return true for the same object.

Parameters:

element - the element to add to this set.

addAll

void addAll(Collection<? extends E> elements)

Adds all of the specified elements to this set if they are not possibly already present.

Parameters:

elements - the elements to add to the set.

mightContain

boolean mightContain(E element)

Checks if the given element might be a member of this set. If this method returns false, then the given object is definitely not a member of the set. If the result is true then the object may or may not be a member of this set, with a certain probability of false positives.

Parameters:

element - the element to check for membership in this set.

Returns:

false if the element is definitely not in the set, or true if it might be.

getStatistics

BloomFilterStatistics getStatistics()

Gets a snapshot of the current statistics of the set.