Package com.googlecode.javaewah.datastructure

Class BitSet

java.lang.Object
com.googlecode.javaewah.datastructure.BitSet
All Implemented Interfaces:
Externalizable, Serializable, Cloneable, Iterable<Integer>
public class BitSet extends Object implements Cloneable, Iterable<Integer>, Externalizable

This is an optimized version of Java's BitSet. In many cases, it can be used as a drop-in replacement.

It differs from the basic Java BitSet class in the following ways:

  • You can iterate over set bits using a simpler syntax for(int bs: myBitset).
  • You can compute the cardinality of an intersection and union without writing it out or modifying your BitSets (see methods such as andcardinality).
  • You can recover wasted memory with trim().
  • It does not implicitly expand: you have to explicitly call resize. This helps to keep memory usage in check.
  • It supports memory-file mapping (see the ImmutableBitSet class).
  • It supports faster and more efficient serialization functions (serialize and deserialize).
Since:
0.8.0
Author:
Daniel Lemire
See Also:
Serialized Form

  • Constructor Summary

    Constructors
    Constructor
    Description
    BitSet()
     
    BitSet​(int sizeInBits)
    Construct a bitset with the specified number of bits (initially all false).

  • Method Summary

    Modifier and Type
    Method
    Description
    void
    and​(com.googlecode.javaewah.datastructure.WordArray bs)
    Compute bitwise AND.
    int
    andcardinality​(com.googlecode.javaewah.datastructure.WordArray bs)
    Compute cardinality of bitwise AND.
    void
    andNot​(com.googlecode.javaewah.datastructure.WordArray bs)
    Compute bitwise AND NOT.
    int
    andNotcardinality​(com.googlecode.javaewah.datastructure.WordArray bs)
    Compute cardinality of bitwise AND NOT.
    static BitSet
    bitmapOf​(int... setBits)
    Return a bitmap with the bit set to true at the given positions.
    int
    cardinality()
    Compute the number of bits set to 1
    void
    clear()
    Reset all bits to false.
    void
    clear​(int index)
    Set the bit to false.
    void
    clear​(int start, int end)
    Set the bits in the range of indexes to false.
    BitSet
    clone()
     
    void
    deserialize​(DataInput in)
    Deserialize.
    boolean
    empty()
    Check whether a bitset contains a set bit.
    boolean
    equals​(Object o)
     
    void
    flip​(int i)
    Flip the bit.
    void
    flip​(int start, int end)
    Flip the bits in the range of indexes.
    boolean
    get​(int i)
    Get the value of the bit.
    int
    getNumberOfWords()
     
    long
    getWord​(int index)
     
    int
    hashCode()
     
    boolean
    intersects​(com.googlecode.javaewah.datastructure.WordArray bs)
    Checks whether two bitsets intersect.
    IntIterator
    intIterator()
    Iterate over the set bits
    Iterator<Integer>
    iterator()
     
    int
    nextSetBit​(int i)
    Usage: for(int i=bs.nextSetBit(0); i>=0; i=bs.nextSetBit(i+1)) { operate on index i here }
    int
    nextUnsetBit​(int i)
    Usage: for(int i=bs.nextUnsetBit(0); i>=0; i=bs.nextUnsetBit(i+1)) { operate on index i here }
    void
    or​(com.googlecode.javaewah.datastructure.WordArray bs)
    Compute bitwise OR.
    int
    orcardinality​(com.googlecode.javaewah.datastructure.WordArray bs)
    Compute cardinality of bitwise OR.
    void
    readExternal​(ObjectInput in)
     
    void
    removeWord​(int i)
    Remove a word.
    void
    resize​(int sizeInBits)
    Resize the bitset
    void
    serialize​(DataOutput out)
    Serialize.
    void
    set​(int i)
    Set to true.
    void
    set​(int i, boolean b)
    Set to some value.
    void
    set​(int start, int end)
    Set the bits in the range of indexes true.
    void
    set​(int start, int end, boolean v)
    Set the bits in the range of indexes to the specified Boolean value.
    int
    size()
    Query the size
    String
    toString()
     
    void
    trim()
    Recovers wasted memory
    void
    unset​(int i)
    Set to false
    IntIterator
    unsetIntIterator()
    Iterate over the unset bits
    void
    writeExternal​(ObjectOutput out)
     
    void
    xor​(com.googlecode.javaewah.datastructure.WordArray bs)
    Compute bitwise XOR.
    int
    xorcardinality​(com.googlecode.javaewah.datastructure.WordArray bs)
    Compute cardinality of bitwise XOR.

    Methods inherited from class java.lang.Object

    finalize, getClass, notify, notifyAll, wait, wait, wait

    Methods inherited from interface java.lang.Iterable

    forEach, spliterator

  • Constructor Details

    • BitSet

      public BitSet​(int sizeInBits)
      Construct a bitset with the specified number of bits (initially all false). The number of bits is rounded up to the nearest multiple of 64.
      Parameters:
      sizeInBits - the size in bits

    • BitSet

      public BitSet()

  • Method Details

    • and

      public void and​(com.googlecode.javaewah.datastructure.WordArray bs)
      Compute bitwise AND.
      Parameters:
      bs - other bitset

    • andcardinality

      public int andcardinality​(com.googlecode.javaewah.datastructure.WordArray bs)
      Compute cardinality of bitwise AND. The current bitmap is modified. Consider calling trim() to recover wasted memory afterward.
      Parameters:
      bs - other bitset
      Returns:
      cardinality

    • andNot

      public void andNot​(com.googlecode.javaewah.datastructure.WordArray bs)
      Compute bitwise AND NOT. The current bitmap is modified. Consider calling trim() to recover wasted memory afterward.
      Parameters:
      bs - other bitset

    • andNotcardinality

      public int andNotcardinality​(com.googlecode.javaewah.datastructure.WordArray bs)
      Compute cardinality of bitwise AND NOT.
      Parameters:
      bs - other bitset
      Returns:
      cardinality

    • cardinality

      public int cardinality()
      Compute the number of bits set to 1
      Returns:
      the number of bits

    • clear

      public void clear()
      Reset all bits to false. This might be wasteful: a better approach is to create a new empty bitmap.

    • clear

      public void clear​(int index)
      Set the bit to false. See unset(int)
      Parameters:
      index - location of the bit

    • clear

      public void clear​(int start, int end)
      Set the bits in the range of indexes to false. This might throw an exception if size() is insufficient, consider calling resize().
      Parameters:
      start - location of the first bit to set to zero
      end - location of the last bit to set to zero (not included)

    • clone

      public BitSet clone()
      Overrides:
      clone in class Object

    • equals

      public boolean equals​(Object o)
      Overrides:
      equals in class Object

    • empty

      public boolean empty()
      Check whether a bitset contains a set bit.
      Returns:
      true if no set bit is found

    • flip

      public void flip​(int i)
      Flip the bit. This might throw an exception if size() is insufficient, consider calling resize().
      Parameters:
      i - index of the bit

    • flip

      public void flip​(int start, int end)
      Flip the bits in the range of indexes. This might throw an exception if size() is insufficient, consider calling resize().
      Parameters:
      start - location of the first bit
      end - location of the last bit (not included)

    • get

      public boolean get​(int i)
      Get the value of the bit. This might throw an exception if size() is insufficient, consider calling resize().
      Parameters:
      i - index
      Returns:
      value of the bit

    • hashCode

      public int hashCode()
      Overrides:
      hashCode in class Object

    • intIterator

      public IntIterator intIterator()
      Iterate over the set bits
      Returns:
      an iterator

    • iterator

      public Iterator<Integer> iterator()
      Specified by:
      iterator in interface Iterable<Integer>

    • intersects

      public boolean intersects​(com.googlecode.javaewah.datastructure.WordArray bs)
      Checks whether two bitsets intersect.
      Parameters:
      bs - other bitset
      Returns:
      true if they have a non-empty intersection (result of AND)

    • nextSetBit

      public int nextSetBit​(int i)
      Usage: for(int i=bs.nextSetBit(0); i>=0; i=bs.nextSetBit(i+1)) { operate on index i here }
      Parameters:
      i - current set bit
      Returns:
      next set bit or -1

    • nextUnsetBit

      public int nextUnsetBit​(int i)
      Usage: for(int i=bs.nextUnsetBit(0); i>=0; i=bs.nextUnsetBit(i+1)) { operate on index i here }
      Parameters:
      i - current unset bit
      Returns:
      next unset bit or -1

    • or

      public void or​(com.googlecode.javaewah.datastructure.WordArray bs)
      Compute bitwise OR. The current bitmap is modified. Consider calling trim() to recover wasted memory afterward.
      Parameters:
      bs - other bitset

    • orcardinality

      public int orcardinality​(com.googlecode.javaewah.datastructure.WordArray bs)
      Compute cardinality of bitwise OR. BitSets are not modified.
      Parameters:
      bs - other bitset
      Returns:
      cardinality

    • removeWord

      public void removeWord​(int i)
      Remove a word.
      Parameters:
      i - index of the word to be removed.

    • resize

      public void resize​(int sizeInBits)
      Resize the bitset
      Parameters:
      sizeInBits - new number of bits

    • set

      public void set​(int i)
      Set to true. This might throw an exception if size() is insufficient, consider calling resize().
      Parameters:
      i - index of the bit

    • set

      public void set​(int i, boolean b)
      Set to some value. This might throw an exception if size() is insufficient, consider calling resize().
      Parameters:
      i - index
      b - value of the bit

    • set

      public void set​(int start, int end)
      Set the bits in the range of indexes true. This might throw an exception if size() is insufficient, consider calling resize().
      Parameters:
      start - location of the first bit
      end - location of the last bit (not included)

    • set

      public void set​(int start, int end, boolean v)
      Set the bits in the range of indexes to the specified Boolean value. This might throw an exception if size() is insufficient, consider calling resize().
      Parameters:
      start - location of the first bit
      end - location of the last bit (not included)
      v - Boolean value

    • size

      public int size()
      Query the size
      Returns:
      the size in bits.

    • trim

      public void trim()
      Recovers wasted memory

    • unset

      public void unset​(int i)
      Set to false
      Parameters:
      i - index of the bit

    • unsetIntIterator

      public IntIterator unsetIntIterator()
      Iterate over the unset bits
      Returns:
      an iterator

    • writeExternal

      public void writeExternal​(ObjectOutput out) throws IOException
      Specified by:
      writeExternal in interface Externalizable
      Throws:
      IOException

    • readExternal

      public void readExternal​(ObjectInput in) throws IOException, ClassNotFoundException
      Specified by:
      readExternal in interface Externalizable
      Throws:
      IOException
      ClassNotFoundException

    • serialize

      public void serialize​(DataOutput out) throws IOException
      Serialize. The current bitmap is not modified.
      Parameters:
      out - the DataOutput stream
      Throws:
      IOException - Signals that an I/O exception has occurred.

    • deserialize

      public void deserialize​(DataInput in) throws IOException
      Deserialize.
      Parameters:
      in - the DataInput stream
      Throws:
      IOException - Signals that an I/O exception has occurred.

    • xor

      public void xor​(com.googlecode.javaewah.datastructure.WordArray bs)
      Compute bitwise XOR. The current bitmap is modified. Consider calling trim() to recover wasted memory afterward.
      Parameters:
      bs - other bitset

    • xorcardinality

      public int xorcardinality​(com.googlecode.javaewah.datastructure.WordArray bs)
      Compute cardinality of bitwise XOR. BitSets are not modified.
      Parameters:
      bs - other bitset
      Returns:
      cardinality

    • getNumberOfWords

      public int getNumberOfWords()

    • getWord

      public long getWord​(int index)

    • bitmapOf

      public static BitSet bitmapOf​(int... setBits)
      Return a bitmap with the bit set to true at the given positions. (This is a convenience method.)
      Parameters:
      setBits - list of set bit positions
      Returns:
      the bitmap

    • toString

      public String toString()
      Overrides:
      toString in class Object