Class BitSet

java.lang.Object
java.util.BitSet
All Implemented Interfaces:
Serializable, Cloneable
public class BitSet extends Object implements Cloneable, Serializable
This class implements a vector of bits that grows as needed. Each component of the bit set has a boolean value. The bits of a BitSet are indexed by nonnegative integers. Individual indexed bits can be examined, set, or cleared. One BitSet may be used to modify the contents of another BitSet through logical AND, logical inclusive OR, and logical exclusive OR operations.

By default, all bits in the set initially have the value false.

Every bit set has a current size, which is the number of bits of space currently in use by the bit set. Note that the size is related to the implementation of a bit set, so it may change with implementation. The length of a bit set relates to logical length of a bit set and is defined independently of implementation.

Unless otherwise noted, passing a null parameter to any of the methods in a BitSet will result in a NullPointerException.

A BitSet is not safe for multithreaded use without external synchronization.

Since:
1.0
See Also:

  • Constructor Summary

    Constructors
    Constructor
    Description
    BitSet()
    Creates a new bit set.
    BitSet(int nbits)
    Creates a bit set whose initial size is large enough to explicitly represent bits with indices in the range 0 through nbits-1.

  • Method Summary

    Modifier and Type
    Method
    Description
    void
    and(BitSet set)
    Performs a logical AND of this target bit set with the argument bit set.
    void
    andNot(BitSet set)
    Clears all of the bits in this BitSet whose corresponding bit is set in the specified BitSet.
    int
    cardinality()
    Returns the number of bits set to true in this BitSet.
    void
    clear()
    Sets all of the bits in this BitSet to false.
    void
    clear(int bitIndex)
    Sets the bit specified by the index to false.
    void
    clear(int fromIndex, int toIndex)
    Sets the bits from the specified fromIndex (inclusive) to the specified toIndex (exclusive) to false.
    Object
    clone()
    Cloning this BitSet produces a new BitSet that is equal to it.
    boolean
    equals(Object obj)
    Compares this bit set against the specified object.
    void
    flip(int bitIndex)
    Sets the bit at the specified index to the complement of its current value.
    void
    flip(int fromIndex, int toIndex)
    Sets each bit from the specified fromIndex (inclusive) to the specified toIndex (exclusive) to the complement of its current value.
    boolean
    get(int bitIndex)
    Returns the value of the bit with the specified index.
    BitSet
    get(int fromIndex, int toIndex)
    Returns a new BitSet composed of bits from this BitSet from fromIndex (inclusive) to toIndex (exclusive).
    int
    hashCode()
    Returns the hash code value for this bit set.
    boolean
    intersects(BitSet set)
    Returns true if the specified BitSet has any bits set to true that are also set to true in this BitSet.
    boolean
    isEmpty()
    Returns true if this BitSet contains no bits that are set to true.
    int
    length()
    Returns the "logical size" of this BitSet: the index of the highest set bit in the BitSet plus one.
    int
    nextClearBit(int fromIndex)
    Returns the index of the first bit that is set to false that occurs on or after the specified starting index.
    int
    nextSetBit(int fromIndex)
    Returns the index of the first bit that is set to true that occurs on or after the specified starting index.
    void
    or(BitSet set)
    Performs a logical OR of this bit set with the bit set argument.
    int
    previousClearBit(int fromIndex)
    Returns the index of the nearest bit that is set to false that occurs on or before the specified starting index.
    int
    previousSetBit(int fromIndex)
    Returns the index of the nearest bit that is set to true that occurs on or before the specified starting index.
    void
    set(int bitIndex)
    Sets the bit at the specified index to true.
    void
    set(int bitIndex, boolean value)
    Sets the bit at the specified index to the specified value.
    void
    set(int fromIndex, int toIndex)
    Sets the bits from the specified fromIndex (inclusive) to the specified toIndex (exclusive) to true.
    void
    set(int fromIndex, int toIndex, boolean value)
    Sets the bits from the specified fromIndex (inclusive) to the specified toIndex (exclusive) to the specified value.
    int
    size()
    Returns the number of bits of space actually in use by this BitSet to represent bit values.
    IntStream
    stream()
    Returns a stream of indices for which this BitSet contains a bit in the set state.
    byte[]
    toByteArray()
    Returns a new byte array containing all the bits in this bit set.
    long[]
    toLongArray()
    Returns a new long array containing all the bits in this bit set.
    String
    toString()
    Returns a string representation of this bit set.
    static BitSet
    valueOf(byte[] bytes)
    Returns a new bit set containing all the bits in the given byte array.
    static BitSet
    valueOf(long[] longs)
    Returns a new bit set containing all the bits in the given long array.
    static BitSet
    valueOf(ByteBuffer bb)
    Returns a new bit set containing all the bits in the given byte buffer between its position and limit.
    static BitSet
    valueOf(LongBuffer lb)
    Returns a new bit set containing all the bits in the given long buffer between its position and limit.
    void
    xor(BitSet set)
    Performs a logical XOR of this bit set with the bit set argument.

    Methods declared in class java.lang.Object

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

  • Constructor Details

    • BitSet

      public BitSet()
      Creates a new bit set. All bits are initially false.

    • BitSet

      public BitSet(int nbits)
      Creates a bit set whose initial size is large enough to explicitly represent bits with indices in the range 0 through nbits-1. All bits are initially false.
      Parameters:
      nbits - the initial size of the bit set
      Throws:
      NegativeArraySizeException - if the specified initial size is negative

  • Method Details

    • valueOf

      public static BitSet valueOf(long[] longs)
      Returns a new bit set containing all the bits in the given long array.

      More precisely,
      BitSet.valueOf(longs).get(n) == ((longs[n/64] & (1L<<(n%64))) != 0)
      for all n < 64 * longs.length.

      This method is equivalent to BitSet.valueOf(LongBuffer.wrap(longs)).

      Parameters:
      longs - a long array containing a little-endian representation of a sequence of bits to be used as the initial bits of the new bit set
      Returns:
      a BitSet containing all the bits in the long array
      Since:
      1.7

    • valueOf

      public static BitSet valueOf(LongBuffer lb)
      Returns a new bit set containing all the bits in the given long buffer between its position and limit.

      More precisely,
      BitSet.valueOf(lb).get(n) == ((lb.get(lb.position()+n/64) & (1L<<(n%64))) != 0)
      for all n < 64 * lb.remaining().

      The long buffer is not modified by this method, and no reference to the buffer is retained by the bit set.

      Parameters:
      lb - a long buffer containing a little-endian representation of a sequence of bits between its position and limit, to be used as the initial bits of the new bit set
      Returns:
      a BitSet containing all the bits in the buffer in the specified range
      Since:
      1.7

    • valueOf

      public static BitSet valueOf(byte[] bytes)
      Returns a new bit set containing all the bits in the given byte array.

      More precisely,
      BitSet.valueOf(bytes).get(n) == ((bytes[n/8] & (1<<(n%8))) != 0)
      for all n < 8 * bytes.length.

      This method is equivalent to BitSet.valueOf(ByteBuffer.wrap(bytes)).

      Parameters:
      bytes - a byte array containing a little-endian representation of a sequence of bits to be used as the initial bits of the new bit set
      Returns:
      a BitSet containing all the bits in the byte array
      Since:
      1.7

    • valueOf

      public static BitSet valueOf(ByteBuffer bb)
      Returns a new bit set containing all the bits in the given byte buffer between its position and limit.

      More precisely,
      BitSet.valueOf(bb).get(n) == ((bb.get(bb.position()+n/8) & (1<<(n%8))) != 0)
      for all n < 8 * bb.remaining().

      The byte buffer is not modified by this method, and no reference to the buffer is retained by the bit set.

      Parameters:
      bb - a byte buffer containing a little-endian representation of a sequence of bits between its position and limit, to be used as the initial bits of the new bit set
      Returns:
      a BitSet containing all the bits in the buffer in the specified range
      Since:
      1.7

    • toByteArray

      public byte[] toByteArray()
      Returns a new byte array containing all the bits in this bit set.

      More precisely, if
      byte[] bytes = s.toByteArray();
      then bytes.length == (s.length()+7)/8 and
      s.get(n) == ((bytes[n/8] & (1<<(n%8))) != 0)
      for all n < 8 * bytes.length.

      Returns:
      a byte array containing a little-endian representation of all the bits in this bit set
      Since:
      1.7

    • toLongArray

      public long[] toLongArray()
      Returns a new long array containing all the bits in this bit set.

      More precisely, if
      long[] longs = s.toLongArray();
      then longs.length == (s.length()+63)/64 and
      s.get(n) == ((longs[n/64] & (1L<<(n%64))) != 0)
      for all n < 64 * longs.length.

      Returns:
      a long array containing a little-endian representation of all the bits in this bit set
      Since:
      1.7

    • flip

      public void flip(int bitIndex)
      Sets the bit at the specified index to the complement of its current value.
      Parameters:
      bitIndex - the index of the bit to flip
      Throws:
      IndexOutOfBoundsException - if the specified index is negative
      Since:
      1.4

    • flip

      public void flip(int fromIndex, int toIndex)
      Sets each bit from the specified fromIndex (inclusive) to the specified toIndex (exclusive) to the complement of its current value.
      Parameters:
      fromIndex - index of the first bit to flip
      toIndex - index after the last bit to flip
      Throws:
      IndexOutOfBoundsException - if fromIndex is negative, or toIndex is negative, or fromIndex is larger than toIndex
      Since:
      1.4

    • set

      public void set(int bitIndex)
      Sets the bit at the specified index to true.
      Parameters:
      bitIndex - a bit index
      Throws:
      IndexOutOfBoundsException - if the specified index is negative
      Since:
      1.0

    • set

      public void set(int bitIndex, boolean value)
      Sets the bit at the specified index to the specified value.
      Parameters:
      bitIndex - a bit index
      value - a boolean value to set
      Throws:
      IndexOutOfBoundsException - if the specified index is negative
      Since:
      1.4

    • set

      public void set(int fromIndex, int toIndex)
      Sets the bits from the specified fromIndex (inclusive) to the specified toIndex (exclusive) to true.
      Parameters:
      fromIndex - index of the first bit to be set
      toIndex - index after the last bit to be set
      Throws:
      IndexOutOfBoundsException - if fromIndex is negative, or toIndex is negative, or fromIndex is larger than toIndex
      Since:
      1.4

    • set

      public void set(int fromIndex, int toIndex, boolean value)
      Sets the bits from the specified fromIndex (inclusive) to the specified toIndex (exclusive) to the specified value.
      Parameters:
      fromIndex - index of the first bit to be set
      toIndex - index after the last bit to be set
      value - value to set the selected bits to
      Throws:
      IndexOutOfBoundsException - if fromIndex is negative, or toIndex is negative, or fromIndex is larger than toIndex
      Since:
      1.4

    • clear

      public void clear(int bitIndex)
      Sets the bit specified by the index to false.
      Parameters:
      bitIndex - the index of the bit to be cleared
      Throws:
      IndexOutOfBoundsException - if the specified index is negative
      Since:
      1.0

    • clear

      public void clear(int fromIndex, int toIndex)
      Sets the bits from the specified fromIndex (inclusive) to the specified toIndex (exclusive) to false.
      Parameters:
      fromIndex - index of the first bit to be cleared
      toIndex - index after the last bit to be cleared
      Throws:
      IndexOutOfBoundsException - if fromIndex is negative, or toIndex is negative, or fromIndex is larger than toIndex
      Since:
      1.4

    • clear

      public void clear()
      Sets all of the bits in this BitSet to false.
      Since:
      1.4

    • get

      public boolean get(int bitIndex)
      Returns the value of the bit with the specified index. The value is true if the bit with the index bitIndex is currently set in this BitSet; otherwise, the result is false.
      Parameters:
      bitIndex - the bit index
      Returns:
      the value of the bit with the specified index
      Throws:
      IndexOutOfBoundsException - if the specified index is negative

    • get

      public BitSet get(int fromIndex, int toIndex)
      Returns a new BitSet composed of bits from this BitSet from fromIndex (inclusive) to toIndex (exclusive).
      Parameters:
      fromIndex - index of the first bit to include
      toIndex - index after the last bit to include
      Returns:
      a new BitSet from a range of this BitSet
      Throws:
      IndexOutOfBoundsException - if fromIndex is negative, or toIndex is negative, or fromIndex is larger than toIndex
      Since:
      1.4

    • nextSetBit

      public int nextSetBit(int fromIndex)
      Returns the index of the first bit that is set to true that occurs on or after the specified starting index. If no such bit exists then -1 is returned.

      To iterate over the true bits in a BitSet, use the following loop: 

       
 for (int i = bs.nextSetBit(0); i >= 0; i = bs.nextSetBit(i+1)) {
     // operate on index i here
     if (i == Integer.MAX_VALUE) {
         break; // or (i+1) would overflow
     }
 }
      Parameters:
      fromIndex - the index to start checking from (inclusive)
      Returns:
      the index of the next set bit, or -1 if there is no such bit
      Throws:
      IndexOutOfBoundsException - if the specified index is negative
      Since:
      1.4

    • nextClearBit

      public int nextClearBit(int fromIndex)
      Returns the index of the first bit that is set to false that occurs on or after the specified starting index.
      Parameters:
      fromIndex - the index to start checking from (inclusive)
      Returns:
      the index of the next clear bit
      Throws:
      IndexOutOfBoundsException - if the specified index is negative
      Since:
      1.4

    • previousSetBit

      public int previousSetBit(int fromIndex)
      Returns the index of the nearest bit that is set to true that occurs on or before the specified starting index. If no such bit exists, or if -1 is given as the starting index, then -1 is returned.

      To iterate over the true bits in a BitSet, use the following loop: 

       
 for (int i = bs.length(); (i = bs.previousSetBit(i-1)) >= 0; ) {
     // operate on index i here
 }
      Parameters:
      fromIndex - the index to start checking from (inclusive)
      Returns:
      the index of the previous set bit, or -1 if there is no such bit
      Throws:
      IndexOutOfBoundsException - if the specified index is less than -1
      Since:
      1.7

    • previousClearBit

      public int previousClearBit(int fromIndex)
      Returns the index of the nearest bit that is set to false that occurs on or before the specified starting index. If no such bit exists, or if -1 is given as the starting index, then -1 is returned.
      Parameters:
      fromIndex - the index to start checking from (inclusive)
      Returns:
      the index of the previous clear bit, or -1 if there is no such bit
      Throws:
      IndexOutOfBoundsException - if the specified index is less than -1
      Since:
      1.7

    • length

      public int length()
      Returns the "logical size" of this BitSet: the index of the highest set bit in the BitSet plus one. Returns zero if the BitSet contains no set bits.
      Returns:
      the logical size of this BitSet
      Since:
      1.2

    • isEmpty

      public boolean isEmpty()
      Returns true if this BitSet contains no bits that are set to true.
      Returns:
      boolean indicating whether this BitSet is empty
      Since:
      1.4

    • intersects

      public boolean intersects(BitSet set)
      Returns true if the specified BitSet has any bits set to true that are also set to true in this BitSet.
      Parameters:
      set - BitSet to intersect with
      Returns:
      boolean indicating whether this BitSet intersects the specified BitSet
      Since:
      1.4

    • cardinality

      public int cardinality()
      Returns the number of bits set to true in this BitSet.
      Returns:
      the number of bits set to true in this BitSet
      Since:
      1.4

    • and

      public void and(BitSet set)
      Performs a logical AND of this target bit set with the argument bit set. This bit set is modified so that each bit in it has the value true if and only if it both initially had the value true and the corresponding bit in the bit set argument also had the value true.
      Parameters:
      set - a bit set

    • or

      public void or(BitSet set)
      Performs a logical OR of this bit set with the bit set argument. This bit set is modified so that a bit in it has the value true if and only if it either already had the value true or the corresponding bit in the bit set argument has the value true.
      Parameters:
      set - a bit set

    • xor

      public void xor(BitSet set)
      Performs a logical XOR of this bit set with the bit set argument. This bit set is modified so that a bit in it has the value true if and only if one of the following statements holds:
      • The bit initially has the value true, and the corresponding bit in the argument has the value false.
      • The bit initially has the value false, and the corresponding bit in the argument has the value true.
      Parameters:
      set - a bit set

    • andNot

      public void andNot(BitSet set)
      Clears all of the bits in this BitSet whose corresponding bit is set in the specified BitSet.
      Parameters:
      set - the BitSet with which to mask this BitSet
      Since:
      1.2

    • hashCode

      public int hashCode()
      Returns the hash code value for this bit set. The hash code depends only on which bits are set within this BitSet.

      The hash code is defined to be the result of the following calculation: 

       
 public int hashCode() {
     long h = 1234;
     long[] words = toLongArray();
     for (int i = words.length; --i >= 0; )
         h ^= words[i] * (i + 1);
     return (int)((h >> 32) ^ h);
 }
      Note that the hash code changes if the set of bits is altered.
      Overrides:
      hashCode in class Object
      Returns:
      the hash code value for this bit set
      See Also:

    • size

      public int size()
      Returns the number of bits of space actually in use by this BitSet to represent bit values. The maximum element in the set is the size - 1st element.
      Returns:
      the number of bits currently in this bit set

    • equals

      public boolean equals(Object obj)
      Compares this bit set against the specified object. The result is true if and only if the argument is not null and is a BitSet object that has exactly the same set of bits set to true as this bit set. That is, for every nonnegative int index k, 
      ((BitSet)obj).get(k) == this.get(k)
      must be true. The current sizes of the two bit sets are not compared.
      Overrides:
      equals in class Object
      Parameters:
      obj - the object to compare with
      Returns:
      true if the objects are the same; false otherwise
      See Also:

    • clone

      public Object clone()
      Cloning this BitSet produces a new BitSet that is equal to it. The clone of the bit set is another bit set that has exactly the same bits set to true as this bit set.
      Overrides:
      clone in class Object
      Returns:
      a clone of this bit set
      See Also:

    • toString

      public String toString()
      Returns a string representation of this bit set. For every index for which this BitSet contains a bit in the set state, the decimal representation of that index is included in the result. Such indices are listed in order from lowest to highest, separated by ", " (a comma and a space) and surrounded by braces, resulting in the usual mathematical notation for a set of integers.

      Example: 

       BitSet drPepper = new BitSet();
      Now drPepper.toString() returns "{}". 
       drPepper.set(2);
      Now drPepper.toString() returns "{2}". 
       drPepper.set(4);
 drPepper.set(10);
      Now drPepper.toString() returns "{2, 4, 10}".
      Overrides:
      toString in class Object
      Returns:
      a string representation of this bit set

    • stream

      public IntStream stream()
      Returns a stream of indices for which this BitSet contains a bit in the set state. The indices are returned in order, from lowest to highest. The size of the stream is the number of bits in the set state, equal to the value returned by the cardinality() method.

      The stream binds to this bit set when the terminal stream operation commences (specifically, the spliterator for the stream is late-binding). If the bit set is modified during that operation then the result is undefined.

      Returns:
      a stream of integers representing set indices
      Since:
      1.8