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## java.util
Class BitSet

    java.lang.Object
      java.util.BitSet

All Implemented Interfaces:
  Cloneable, Serializable

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:
  JDK1.0
See Also:
  Serialized Form

Constructor Summary
`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
`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 object against the specified object.
`void` | `flip(int bitIndex)` Sets the bit at the specified index to 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 a 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.
`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.
`String` | `toString()` Returns a string representation of this bit set.
`void` | `xor(BitSet set)` Performs a logical XOR of this bit set with the bit set argument.

Methods inherited from class java.lang.Object
`finalize, getClass, notify, notifyAll, wait, wait, wait`

Constructor Detail

### 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 Detail

### flip

    public void flip(int bitIndex)

  Sets the bit at the specified index to 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:
    JDK1.0

### 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:
    JDK1.0

### 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 }

  Parameters:
    `fromIndex` - the index to start checking from (inclusive).
  Returns:
    the index of the next set 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

### 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:
    JDK1.2

### hashCode

    public int hashCode()

  Returns a hash code value for this bit set. The has code depends only on which bits have been set within this `BitSet`. The algorithm used to compute it may be described as follows.

  Suppose the bits in the `BitSet` were to be stored in an array of `long` integers called, say, `bits`, in such a manner that bit `k` is set in the `BitSet` (for nonnegative values of `k`) if and only if the expression

      ((k>>6) < bits.length) && ((bits[k>>6] & (1L << (bit & 0x3F))) != 0)

  is true. Then the following definition of the `hashCode` method would be a correct implementation of the actual algorithm:

       public int hashCode() {
            long h = 1234;
            for (int i = bits.length; --i >= 0; ) {
                 h ^= bits[i] * (i + 1);
            }
            return (int)((h >> 32) ^ h);
       }

  Note that the hash code values change if the set of bits is altered.

  Overrides the `hashCode` method of `Object`.

  Overrides:
    `hashCode` in class `Object`
  Returns:
    a hash code value for this bit set.
  See Also:
    `Object.equals(java.lang.Object)`, `Hashtable`

### 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 object 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 the `equals` method of `Object`.

  Overrides:
    `equals` in class `Object`
  Parameters:
    `obj` - the object to compare with.
  Returns:
    `true` if the objects are the same; `false` otherwise.
  See Also:
    `size()`

### 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 and the same current size.

  Overrides the `clone` method of `Object`.

  Overrides:
    `clone` in class `Object`
  Returns:
    a clone of this bit set.
  See Also:
    `size()`

### 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.

  Overrides the `toString` method of `Object`.

  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.

Overview | Package | Class | Use | Tree | Deprecated | Index | Help
| JavaTM 2 Platform Std. Ed. v1.4.2
PREV CLASS NEXT CLASS | FRAMES NO FRAMES
SUMMARY: NESTED | FIELD | CONSTR | METHOD | DETAIL: FIELD | CONSTR | METHOD

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For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

Copyright 2003 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.