# Class LayeredBloomFilter<T extends BloomFilter<T>>

java.lang.Object
org.apache.commons.collections4.bloomfilter.LayeredBloomFilter<T>

Type Parameters:
  `T` - The type of Bloom Filter that is used for the layers.

All Implemented Interfaces:
  `BitMapExtractor`, `BloomFilter<LayeredBloomFilter<T>>`, `BloomFilterExtractor`, `IndexExtractor`

public class LayeredBloomFilter<T extends BloomFilter<T>> extends Object implements BloomFilter<LayeredBloomFilter<T>>, BloomFilterExtractor
Layered Bloom filters are described in Zhiwang, Cen; Jungang, Xu; Jian, Sun (2010), "A multi-layer Bloom filter for duplicated URL detection", Proc. 3rd International Conference on Advanced Computer Theory and Engineering (ICACTE 2010), vol. 1, pp. V1-586-V1-591, doi:10.1109/ICACTE.2010.5578947, ISBN 978-1-4244-6539-2, S2CID 3108985

In short, Layered Bloom filter contains several bloom filters arranged in layers.

- When membership in the filter is checked each layer in turn is checked and if a match is found `true` is returned.
- When merging each bloom filter is merged into the newest filter in the list of layers.
- When questions of cardinality are asked the cardinality of the union of the enclosed Bloom filters is used.

The net result is that the layered Bloom filter can be populated with more items than the Shape would indicate and yet still return a false positive rate in line with the Shape and not the over population.

This implementation uses a LayerManager to handle the manipulation of the layers.

- Level 0 is the oldest layer and the highest level is the newest.
- There is always at least one enclosed filter.
- The newest filter is the `target` into which merges are performed.
- Whenever the target is retrieved, or a `merge` operation is performed the code checks if any older layers should be removed, and if so removes them. It also checks it a new layer should be added, and if so adds it and sets the `target` before the operation.

Since:
  4.5.0-M2

- ## Field Summary

  ### Fields inherited from interface org.apache.commons.collections4.bloomfilter.BloomFilter

  `SPARSE`

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `LayeredBloomFilter(Shape shape, LayerManager<T> layerManager)`
  Constructs a new instance.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `int`
  `cardinality()`
  Gets the cardinality (number of enabled bits) of this Bloom filter.
  `int`
  `characteristics()`
  Gets the characteristics of the filter.
  `void`
  `cleanup()`
  Forces the execution of the cleanup Consumer that was provided when the associated LayerManager was built.
  `final void`
  `clear()`
  Clears the filter to by resetting it to its initial, unpopulated state.
  `boolean`
  `contains(BitMapExtractor bitMapExtractor)`
  Returns `true` if this filter contains the bits specified in the bit maps produced by the bitMapExtractor.
  `boolean`
  `contains(BloomFilter other)`
  Returns `true` if this any layer contained by this filter contains the specified filter.
  `boolean`
  `contains(BloomFilterExtractor bloomFilterExtractor)`
  Returns `true` if each filter within the `bloomFilterExtractor` exits within this filter.
  `boolean`
  `contains(Hasher hasher)`
  Returns `true` if this filter contains the bits specified in the hasher.
  `boolean`
  `contains(IndexExtractor indexExtractor)`
  Returns `true` if this filter contains the indices specified IndexExtractor.
  `LayeredBloomFilter<T>`
  `copy()`
  Creates a new instance of this `LayeredBloomFilter` with the same properties as the current one.
  `int`
  `estimateN()`
  Estimates the number of items in the Bloom filter.
  `int`
  `estimateUnion(BloomFilter other)`
  Estimates the number of items in the union of this Bloom filter with the other bloom filter.
  `int[]`
  `find(BitMapExtractor bitMapExtractor)`
  Finds the layers in which the BitMapExtractor is found.
  `int[]`
  `find(BloomFilter bf)`
  Finds the layers in which the Bloom filter is found.
  `int[]`
  `find(Hasher hasher)`
  Finds the layers in which the Hasher is found.
  `int[]`
  `find(IndexExtractor indexExtractor)`
  Finds the layers in which the IndexExtractor is found.
  `SimpleBloomFilter`
  `flatten()`
  Create a standard (non-layered) Bloom filter by merging all of the layers.
  `T`
  `get(int depth)`
  Gets the Bloom filter at the specified depth
  `final int`
  `getDepth()`
  Gets the depth of the deepest layer.
  `final Shape`
  `getShape()`
  Gets the shape that was used when the filter was built.
  `boolean`
  `isEmpty()`
  Determines if all the bits are off.
  `boolean`
  `merge(BitMapExtractor bitMapExtractor)`
  Merges the specified hasher into this Bloom filter.
  `boolean`
  `merge(BloomFilter bf)`
  Merges the specified Bloom filter into this Bloom filter.
  `boolean`
  `merge(IndexExtractor indexExtractor)`
  Merges the specified IndexExtractor into this Bloom filter.
  `void`
  `next()`
  Forces and advance to the next layer.
  `boolean`
  `processBitMaps(LongPredicate predicate)`
  Each bit map is passed to the predicate in order.
  `final boolean`
  `processBloomFilters(Predicate<BloomFilter> bloomFilterPredicate)`
  Processes the Bloom filters in depth order with the most recent filters first.
  `boolean`
  `processIndices(IntPredicate predicate)`
  Each index is passed to the predicate.

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

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

  ### Methods inherited from interface org.apache.commons.collections4.bloomfilter.BitMapExtractor

  `asBitMapArray, processBitMapPairs`

  ### Methods inherited from interface org.apache.commons.collections4.bloomfilter.BloomFilter

  `estimateIntersection, isFull, merge, uniqueIndices`

  ### Methods inherited from interface org.apache.commons.collections4.bloomfilter.BloomFilterExtractor

  `asBloomFilterArray, processBloomFilterPair`

  ### Methods inherited from interface org.apache.commons.collections4.bloomfilter.IndexExtractor

  `asIndexArray`

- ## Constructor Details

  - ### LayeredBloomFilter

    public LayeredBloomFilter(Shape shape, LayerManager<T> layerManager)
    Constructs a new instance.
    Parameters:
      `shape` - the Shape of the enclosed Bloom filters
      `layerManager` - the LayerManager to manage the layers.

- ## Method Details

  - ### cardinality

    public int cardinality()
    Description copied from interface: `BloomFilter`
    Gets the cardinality (number of enabled bits) of this Bloom filter.

    This is also known as the Hamming value or Hamming number.

    Specified by:
      `cardinality` in interface `BloomFilter<T extends BloomFilter<T>>`
    Returns:
      the cardinality of this filter

  - ### characteristics

    public int characteristics()
    Description copied from interface: `BloomFilter`
    Gets the characteristics of the filter.

    Characteristics are defined as bits within the characteristics integer.

    Specified by:
      `characteristics` in interface `BloomFilter<T extends BloomFilter<T>>`
    Returns:
      the characteristics for this bloom filter.

  - ### cleanup

    public void cleanup()
    Forces the execution of the cleanup Consumer that was provided when the associated LayerManager was built.
    See Also:
      - `LayerManager.Builder.setCleanup(java.util.function.Consumer)`

  - ### clear

    public final void clear()
    Description copied from interface: `BloomFilter`
    Clears the filter to by resetting it to its initial, unpopulated state.
    Specified by:
      `clear` in interface `BloomFilter<T extends BloomFilter<T>>`

  - ### contains

    public boolean contains(BitMapExtractor bitMapExtractor)
    Description copied from interface: `BloomFilter`
    Returns `true` if this filter contains the bits specified in the bit maps produced by the bitMapExtractor.
    Specified by:
      `contains` in interface `BloomFilter<T extends BloomFilter<T>>`
    Parameters:
      `bitMapExtractor` - the `BitMapExtractor` to provide the bit maps.
    Returns:
      `true` if this filter is enabled for all bits specified by the bit maps

  - ### contains

    public boolean contains(BloomFilter other)
    Returns `true` if this any layer contained by this filter contains the specified filter.

    If the `other` is a BloomFilterExtractor each filter within the `other` is checked to see if it exits within this filter.

    Specified by:
      `contains` in interface `BloomFilter<T extends BloomFilter<T>>`
    Parameters:
      `other` - the other Bloom filter
    Returns:
      `true` if this filter contains the other filter.

  - ### contains

    public boolean contains(BloomFilterExtractor bloomFilterExtractor)
    Returns `true` if each filter within the `bloomFilterExtractor` exits within this filter.
    Parameters:
      `bloomFilterExtractor` - the BloomFilterExtractor that provides the filters to check for.
    Returns:
      `true` if this filter contains all of the filters contained in the `bloomFilterExtractor`.

  - ### contains

    public boolean contains(Hasher hasher)
    Description copied from interface: `BloomFilter`
    Returns `true` if this filter contains the bits specified in the hasher.

    Specifically this returns `true` if this filter is enabled for all bit indexes identified by the `hasher`. Using the bit map representations this is effectively `(this AND hasher) == hasher`.

    Specified by:
      `contains` in interface `BloomFilter<T extends BloomFilter<T>>`
    Parameters:
      `hasher` - the hasher to provide the indexes
    Returns:
      true if this filter is enabled for all bits specified by the hasher

  - ### contains

    public boolean contains(IndexExtractor indexExtractor)
    Description copied from interface: `BloomFilter`
    Returns `true` if this filter contains the indices specified IndexExtractor.

    Specifically this returns `true` if this filter is enabled for all bit indexes identified by the `IndexExtractor`.

    Specified by:
      `contains` in interface `BloomFilter<T extends BloomFilter<T>>`
    Parameters:
      `indexExtractor` - the IndexExtractor to provide the indexes
    Returns:
      `true` if this filter is enabled for all bits specified by the IndexExtractor

  - ### copy

    public LayeredBloomFilter<T> copy()
    Creates a new instance of this `LayeredBloomFilter` with the same properties as the current one.
    Specified by:
      `copy` in interface `BloomFilter<T extends BloomFilter<T>>`
    Returns:
      a copy of this `LayeredBloomFilter`.

  - ### estimateN

    public int estimateN()
    Description copied from interface: `BloomFilter`
    Estimates the number of items in the Bloom filter.

    By default this is the rounding of the `Shape.estimateN(cardinality)` calculation for the shape and cardinality of this filter.

    This produces an estimate roughly equivalent to the number of Hashers that have been merged into the filter by rounding the value from the calculation described in the `Shape` class Javadoc.

    Note:

    - if cardinality == numberOfBits, then result is Integer.MAX_VALUE.
    - if cardinality > numberOfBits, then an IllegalArgumentException is thrown.
    Specified by:
      `estimateN` in interface `BloomFilter<T extends BloomFilter<T>>`
    Returns:
      an estimate of the number of items in the bloom filter. Will return Integer.MAX_VALUE if the estimate is larger than Integer.MAX_VALUE.
    See Also:
      - `Shape.estimateN(int)`
      - `Shape`

  - ### estimateUnion

    public int estimateUnion(BloomFilter other)
    Description copied from interface: `BloomFilter`
    Estimates the number of items in the union of this Bloom filter with the other bloom filter.

    This produces an estimate roughly equivalent to the number of unique Hashers that have been merged into either of the filters by rounding the value from the calculation described in the `Shape` class Javadoc.

    `estimateUnion` should only be called with Bloom filters of the same Shape. If called on Bloom filters of differing shape this method is not symmetric. If `other` has more bits an `IllegalArgumentException` may be thrown.

    Specified by:
      `estimateUnion` in interface `BloomFilter<T extends BloomFilter<T>>`
    Parameters:
      `other` - The other Bloom filter
    Returns:
      an estimate of the number of items in the union. Will return Integer.MAX_VALUE if the estimate is larger than Integer.MAX_VALUE.
    See Also:
      - `BloomFilter.estimateN()`
      - `Shape`

  - ### find

    public int[] find(BitMapExtractor bitMapExtractor)
    Finds the layers in which the BitMapExtractor is found.
    Parameters:
      `bitMapExtractor` - the BitMapExtractor to search for.
    Returns:
      an array of layer indices in which the Bloom filter is found.

  - ### find

    public int[] find(BloomFilter bf)
    Finds the layers in which the Bloom filter is found.
    Parameters:
      `bf` - the Bloom filter to search for.
    Returns:
      an array of layer indices in which the Bloom filter is found.

  - ### find

    public int[] find(Hasher hasher)
    Finds the layers in which the Hasher is found.
    Parameters:
      `hasher` - the Hasher to search for.
    Returns:
      an array of layer indices in which the Bloom filter is found.

  - ### find

    public int[] find(IndexExtractor indexExtractor)
    Finds the layers in which the IndexExtractor is found.
    Parameters:
      `indexExtractor` - the Index extractor to search for.
    Returns:
      an array of layer indices in which the Bloom filter is found.

  - ### flatten

    public SimpleBloomFilter flatten()
    Create a standard (non-layered) Bloom filter by merging all of the layers. If the filter is empty this method will return an empty Bloom filter.
    Specified by:
      `flatten` in interface `BloomFilterExtractor`
    Returns:
      the merged bloom filter.

  - ### get

    public T get(int depth)
    Gets the Bloom filter at the specified depth
    Parameters:
      `depth` - the depth of the filter to return.
    Returns:
      the Bloom filter at the specified depth.
    Throws:
      `NoSuchElementException` - if depth is not in the range [0,getDepth())

  - ### getDepth

    public final int getDepth()
    Gets the depth of the deepest layer. The minimum value returned by this method is 1.
    Returns:
      the depth of the deepest layer.

  - ### getShape

    public final Shape getShape()
    Description copied from interface: `BloomFilter`
    Gets the shape that was used when the filter was built.
    Specified by:
      `getShape` in interface `BloomFilter<T extends BloomFilter<T>>`
    Returns:
      The shape the filter was built with.

  - ### isEmpty

    public boolean isEmpty()
    Description copied from interface: `BloomFilter`
    Determines if all the bits are off. This is equivalent to `cardinality() == 0`.

    Note: This method is optimized for non-sparse filters. Implementers are encouraged to implement faster checks if possible.

    Specified by:
      `isEmpty` in interface `BloomFilter<T extends BloomFilter<T>>`
    Returns:
      `true` if no bits are enabled, `false` otherwise.

  - ### merge

    public boolean merge(BitMapExtractor bitMapExtractor)
    Description copied from interface: `BloomFilter`
    Merges the specified hasher into this Bloom filter. Specifically all bit indexes that are identified by the `bitMapExtractor` will be enabled in this filter.

    Note: This method should return `true` even if no additional bit indexes were enabled. A `false` result indicates that this filter may or may not contain all the indexes enabled in the `bitMapExtractor`. This state may occur in complex Bloom filter implementations like counting Bloom filters.

    Specified by:
      `merge` in interface `BloomFilter<T extends BloomFilter<T>>`
    Parameters:
      `bitMapExtractor` - The BitMapExtractor to merge.
    Returns:
      true if the merge was successful

  - ### merge

    public boolean merge(BloomFilter bf)
    Description copied from interface: `BloomFilter`
    Merges the specified Bloom filter into this Bloom filter.

    Specifically all bit indexes that are identified by the `other` will be enabled in this filter.

    Note: This method should return `true` even if no additional bit indexes were enabled. A `false` result indicates that this filter may or may not contain the `other` Bloom filter. This state may occur in complex Bloom filter implementations like counting Bloom filters.

    Specified by:
      `merge` in interface `BloomFilter<T extends BloomFilter<T>>`
    Parameters:
      `bf` - The bloom filter to merge into this one.
    Returns:
      true if the merge was successful

  - ### merge

    public boolean merge(IndexExtractor indexExtractor)
    Description copied from interface: `BloomFilter`
    Merges the specified IndexExtractor into this Bloom filter. Specifically all bit indexes that are identified by the `indexExtractor` will be enabled in this filter.

    Note: This method should return `true` even if no additional bit indexes were enabled. A `false` result indicates that this filter may or may not contain all the indexes of the `indexExtractor`. This state may occur in complex Bloom filter implementations like counting Bloom filters.

    Specified by:
      `merge` in interface `BloomFilter<T extends BloomFilter<T>>`
    Parameters:
      `indexExtractor` - The IndexExtractor to merge.
    Returns:
      true if the merge was successful

  - ### next

    public void next()
    Forces and advance to the next layer. This method will clean-up the current layers and generate a new filter layer. In most cases is it unnecessary to call this method directly.
    See Also:
      - `LayerManager.Builder.setCleanup(java.util.function.Consumer)`
      - `LayerManager.Builder.setExtendCheck(Predicate)`

  - ### processBitMaps

    public boolean processBitMaps(LongPredicate predicate)
    Description copied from interface: `BitMapExtractor`
    Each bit map is passed to the predicate in order. The predicate is applied to each bit map value, if the predicate returns `false` the execution is stopped, `false` is returned, and no further bit maps are processed.

    If the extractor is empty this method will return true.

    Any exceptions thrown by the action are relayed to the caller.

    Specified by:
      `processBitMaps` in interface `BitMapExtractor`
    Parameters:
      `predicate` - the function to execute
    Returns:
      `true` if all bit maps returned `true`, `false` otherwise.

  - ### processBloomFilters

    public final boolean processBloomFilters(Predicate<BloomFilter> bloomFilterPredicate)
    Processes the Bloom filters in depth order with the most recent filters first. Each filter is passed to the predicate in turn. The function exits on the first `false` returned by the predicate.
    Specified by:
      `processBloomFilters` in interface `BloomFilterExtractor`
    Parameters:
      `bloomFilterPredicate` - the predicate to execute.
    Returns:
      `true` if all filters passed the predicate, `false` otherwise.

  - ### processIndices

    public boolean processIndices(IntPredicate predicate)
    Description copied from interface: `IndexExtractor`
    Each index is passed to the predicate. The predicate is applied to each index value, if the predicate returns `false` the execution is stopped, `false` is returned, and no further indices are processed.

    Any exceptions thrown by the action are relayed to the caller.

    Indices ordering and uniqueness is not guaranteed.

    Specified by:
      `processIndices` in interface `IndexExtractor`
    Parameters:
      `predicate` - the action to be performed for each non-zero bit index.
    Returns:
      `true` if all indexes return true from consumer, `false` otherwise.