com.sun.squawk.util
Class BitSet

java.lang.Object
  com.sun.squawk.util.BitSet

public final class BitSet
extends Object

This class provides mechanisms for manipulating a bit set.

Constructor Summary

BitSet()
Creates a new BitSet instance whose underlying byte array is controlled by the instance.

BitSet(byte[] bits)
Creates a new BitSet instance whose underlying byte array is controlled by the client of the instance.

Method Summary

boolean	areBitsExternal()
int	cardinality() Returns the number of bits set to 1 in this BitSet.
void	clear() Clears all of the bits in this BitSet.
void	clear(int bitIndex) Clears the bit at a given index.
void	copyInto(byte[] bits) Copies the bit set representation into a provided byte array.
boolean	equals(Object obj) Compares this object against the specified object.
boolean	get(int bitIndex) Returns the value of the bit with the specified index.
int	hashCode() Returns a hash code value for this bit set.
int	length() Returns the "logical size" of this BitSet: the index of the highest set bit in the BitSet plus one.
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 other) Performs a logical OR of this bit set with the bit set argument.
void	or(BitSet other, int shift) Performs a logical OR of this bit set with a given bit set.
void	set(int bitIndex) Sets the bit at a given index.
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.
protected void	validateIndex(int bitIndex) Determines if a given bit index is valid.

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

BitSet

public BitSet()

Creates a new BitSet instance whose underlying byte array is controlled by the instance. Only this type of BitSet will grow as necessary and will never throw an IndexOutOfBoundsException if a given bitIndex is greater than the current physical size of the underlying byte array.

BitSet

public BitSet(byte[] bits)

Creates a new BitSet instance whose underlying byte array is controlled by the client of the instance. This type of BitSet will throw an IndexOutOfBoundsException if a given bitIndex is greater than the highest bit that can be expressed in the underlying byte array.

Parameters:

bits - the underlying byte array

Method Detail

areBitsExternal

public boolean areBitsExternal()

validateIndex

protected void validateIndex(int bitIndex)

Determines if a given bit index is valid.

Parameters:

bitIndex - the bit index to test

Throws:

IndexOutOfBoundsException - is the given index is negative

copyInto

public void copyInto(byte[] bits)

Copies the bit set representation into a provided byte array. The number of bytes copied is equal to the minimum of length of the provided byte array and the internal byte array.

Parameters:

bits - the byte array to copy into

Throws:

NullPointerException - if the given buffer is null.

length

public int length()

Returns the "logical size" of this BitSet: the index of the highest set bit in the BitSet plus one.

Returns:

the logical size of this BitSet.

size

public int size()

Returns the number of bits of space actually in use by this BitSet to represent bit values.

Returns:

the number of bits currently in this bit set.

set

public void set(int bitIndex)

Sets the bit at a given index.

Parameters:

bitIndex - the index of the bit to set

Throws:

IndexOutOfBoundsException - if the given bit index is negative or if this is an external BitSet instance and bitIndex >= this.size()

clear

public void clear(int bitIndex)

Clears the bit at a given index.

Parameters:

bitIndex - the index of the bit to clear

Throws:

IndexOutOfBoundsException - if the given bit index is negative

clear

public void clear()

Clears all of the bits in this BitSet.

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 given bit index is negative

cardinality

public int cardinality()

Returns the number of bits set to 1 in this BitSet.

Returns:

the number of bits set to 1 in this BitSet.

or

public void or(BitSet other)

Performs a logical OR of this bit set with the bit set argument. This bit set is modified so that a bit at index n in this set is 1 if and only if it was already set or the bit at index n in other was set. The semantics of this operation can be expressed as:

      this = this | other;
 

Parameters:

other - a bit set

or

public void or(BitSet other,
               int shift)

Performs a logical OR of this bit set with a given bit set. The semantics of this operation can be expressed as:

      this = this | (other >= 0 ? other << offset : other >> offset);
 

Parameters:

other - a bit set

shift - the amount by which other should be logically shifted before being or'ed with 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:

BitSet.size()

hashCode

public int hashCode()

Returns a hash code value for this bit set.

Overrides:

hashCode in class Object

Returns:

a hash code value for this bit set.

See Also:

Object.equals(java.lang.Object), Hashtable

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 use the following loop:

 for (int i = oopMap.nextSetBit(0); i >= 0; i = oopMap.nextSetBit(i + 1)) {
     // operate on index i here
 }
 

Parameters:

fromIndex - the index to start checking from (inclusive). This must be positive

Returns:

the index of the next set bit.

Throws:

IndexOutOfBoundsException - if the specified index is negative.

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.