File	Doc	Category	Size	Date	Package
BitSet.java	API Doc	Java SE 6 API	30549	Tue Jun 10 00:25:52 BST 2008	java.util

BitSet

• java.lang.Object

Fields Summary
private static final int	ADDRESS_BITS_PER_WORD
private static final int	BITS_PER_WORD
private static final int	BIT_INDEX_MASK
private static final long	WORD_MASK
private static final ObjectStreamField[]	serialPersistentFields
private long[]	words The internal field corresponding to the serialField "bits".
private transient int	wordsInUse The number of words in the logical size of this BitSet.
private transient boolean	sizeIsSticky Whether the size of "words" is user-specified. If so, we assume the user knows what he's doing and try harder to preserve it.
private static final long	serialVersionUID

Constructors Summary
public BitSet() Creates a new bit set. All bits are initially false. initWords(BITS_PER_WORD); sizeIsSticky = false;
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. param nbits the initial size of the bit set. exception NegativeArraySizeException if the specified initial size is negative. // nbits can't be negative; size 0 is OK if (nbits < 0) throw new NegativeArraySizeException("nbits < 0: " + nbits); initWords(nbits); sizeIsSticky = true;

Methods Summary
public void	and(java.util.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. param set a bit set. if (this == set) return; while (wordsInUse > set.wordsInUse) words[--wordsInUse] = 0; // Perform logical AND on words in common for (int i = 0; i < wordsInUse; i++) words[i] &= set.words[i]; recalculateWordsInUse(); checkInvariants();
public void	andNot(java.util.BitSet set) Clears all of the bits in this BitSet whose corresponding bit is set in the specified BitSet. param set the BitSet with which to mask this BitSet. since 1.2 // Perform logical (a & !b) on words in common for (int i = Math.min(wordsInUse, set.wordsInUse) - 1; i >= 0; i--) words[i] &= ~set.words[i]; recalculateWordsInUse(); checkInvariants();
public int	cardinality() Returns the number of bits set to true in this BitSet. return the number of bits set to true in this BitSet. since 1.4 int sum = 0; for (int i = 0; i < wordsInUse; i++) sum += Long.bitCount(words[i]); return sum;
private void	checkInvariants() Every public method must preserve these invariants. assert(wordsInUse == 0 || words[wordsInUse - 1] != 0); assert(wordsInUse >= 0 && wordsInUse <= words.length); assert(wordsInUse == words.length || words[wordsInUse] == 0);
private static void	checkRange(int fromIndex, int toIndex) Checks that fromIndex ... toIndex is a valid range of bit indices. if (fromIndex < 0) throw new IndexOutOfBoundsException("fromIndex < 0: " + fromIndex); if (toIndex < 0) throw new IndexOutOfBoundsException("toIndex < 0: " + toIndex); if (fromIndex > toIndex) throw new IndexOutOfBoundsException("fromIndex: " + fromIndex + " > toIndex: " + toIndex);
public void	clear(int bitIndex) Sets the bit specified by the index to false. param bitIndex the index of the bit to be cleared. exception IndexOutOfBoundsException if the specified index is negative. since JDK1.0 if (bitIndex < 0) throw new IndexOutOfBoundsException("bitIndex < 0: " + bitIndex); int wordIndex = wordIndex(bitIndex); if (wordIndex >= wordsInUse) return; words[wordIndex] &= ~(1L << bitIndex); recalculateWordsInUse(); checkInvariants();
public void	clear(int fromIndex, int toIndex) Sets the bits from the specified fromIndex (inclusive) to the specified toIndex (exclusive) to false. param fromIndex index of the first bit to be cleared. param toIndex index after the last bit to be cleared. exception IndexOutOfBoundsException if fromIndex is negative, or toIndex is negative, or fromIndex is larger than toIndex. since 1.4 checkRange(fromIndex, toIndex); if (fromIndex == toIndex) return; int startWordIndex = wordIndex(fromIndex); if (startWordIndex >= wordsInUse) return; int endWordIndex = wordIndex(toIndex - 1); if (endWordIndex >= wordsInUse) { toIndex = length(); endWordIndex = wordsInUse - 1; } long firstWordMask = WORD_MASK << fromIndex; long lastWordMask = WORD_MASK >>> -toIndex; if (startWordIndex == endWordIndex) { // Case 1: One word words[startWordIndex] &= ~(firstWordMask & lastWordMask); } else { // Case 2: Multiple words // Handle first word words[startWordIndex] &= ~firstWordMask; // Handle intermediate words, if any for (int i = startWordIndex+1; i < endWordIndex; i++) words[i] = 0; // Handle last word words[endWordIndex] &= ~lastWordMask; } recalculateWordsInUse(); checkInvariants();
public void	clear() Sets all of the bits in this BitSet to false. since 1.4 while (wordsInUse > 0) words[--wordsInUse] = 0;
public java.lang.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 the clone method of Object. return a clone of this bit set. see java.util.BitSet#size() if (! sizeIsSticky) trimToSize(); try { BitSet result = (BitSet) super.clone(); result.words = words.clone(); result.checkInvariants(); return result; } catch (CloneNotSupportedException e) { throw new InternalError(); }
private void	ensureCapacity(int wordsRequired) Ensures that the BitSet can hold enough words. param wordsRequired the minimum acceptable number of words. if (words.length < wordsRequired) { // Allocate larger of doubled size or required size int request = Math.max(2 * words.length, wordsRequired); words = Arrays.copyOf(words, request); sizeIsSticky = false; }
public boolean	equals(java.lang.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. param obj the object to compare with. return true if the objects are the same; false otherwise. see java.util.BitSet#size() if (!(obj instanceof BitSet)) return false; if (this == obj) return true; BitSet set = (BitSet) obj; checkInvariants(); set.checkInvariants(); if (wordsInUse != set.wordsInUse) return false; // Check words in use by both BitSets for (int i = 0; i < wordsInUse; i++) if (words[i] != set.words[i]) return false; return true;
private void	expandTo(int wordIndex) Ensures that the BitSet can accommodate a given wordIndex, temporarily violating the invariants. The caller must restore the invariants before returning to the user, possibly using recalculateWordsInUse(). param wordIndex the index to be accommodated. int wordsRequired = wordIndex+1; if (wordsInUse < wordsRequired) { ensureCapacity(wordsRequired); wordsInUse = wordsRequired; }
public void	flip(int bitIndex) Sets the bit at the specified index to the complement of its current value. param bitIndex the index of the bit to flip. exception IndexOutOfBoundsException if the specified index is negative. since 1.4 if (bitIndex < 0) throw new IndexOutOfBoundsException("bitIndex < 0: " + bitIndex); int wordIndex = wordIndex(bitIndex); expandTo(wordIndex); words[wordIndex] ^= (1L << bitIndex); recalculateWordsInUse(); checkInvariants();
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. param fromIndex index of the first bit to flip. param toIndex index after the last bit to flip. exception IndexOutOfBoundsException if fromIndex is negative, or toIndex is negative, or fromIndex is larger than toIndex. since 1.4 checkRange(fromIndex, toIndex); if (fromIndex == toIndex) return; int startWordIndex = wordIndex(fromIndex); int endWordIndex = wordIndex(toIndex - 1); expandTo(endWordIndex); long firstWordMask = WORD_MASK << fromIndex; long lastWordMask = WORD_MASK >>> -toIndex; if (startWordIndex == endWordIndex) { // Case 1: One word words[startWordIndex] ^= (firstWordMask & lastWordMask); } else { // Case 2: Multiple words // Handle first word words[startWordIndex] ^= firstWordMask; // Handle intermediate words, if any for (int i = startWordIndex+1; i < endWordIndex; i++) words[i] ^= WORD_MASK; // Handle last word words[endWordIndex] ^= lastWordMask; } recalculateWordsInUse(); checkInvariants();
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. param bitIndex the bit index. return the value of the bit with the specified index. exception IndexOutOfBoundsException if the specified index is negative. if (bitIndex < 0) throw new IndexOutOfBoundsException("bitIndex < 0: " + bitIndex); checkInvariants(); int wordIndex = wordIndex(bitIndex); return (wordIndex < wordsInUse) && ((words[wordIndex] & (1L << bitIndex)) != 0);
public java.util.BitSet	get(int fromIndex, int toIndex) Returns a new BitSet composed of bits from this BitSet from fromIndex (inclusive) to toIndex (exclusive). param fromIndex index of the first bit to include. param toIndex index after the last bit to include. return a new BitSet from a range of this BitSet. exception IndexOutOfBoundsException if fromIndex is negative, or toIndex is negative, or fromIndex is larger than toIndex. since 1.4 checkRange(fromIndex, toIndex); checkInvariants(); int len = length(); // If no set bits in range return empty bitset if (len <= fromIndex || fromIndex == toIndex) return new BitSet(0); // An optimization if (toIndex > len) toIndex = len; BitSet result = new BitSet(toIndex - fromIndex); int targetWords = wordIndex(toIndex - fromIndex - 1) + 1; int sourceIndex = wordIndex(fromIndex); boolean wordAligned = ((fromIndex & BIT_INDEX_MASK) == 0); // Process all words but the last word for (int i = 0; i < targetWords - 1; i++, sourceIndex++) result.words[i] = wordAligned ? words[sourceIndex] : (words[sourceIndex] >>> fromIndex) | (words[sourceIndex+1] << -fromIndex); // Process the last word long lastWordMask = WORD_MASK >>> -toIndex; result.words[targetWords - 1] = ((toIndex-1) & BIT_INDEX_MASK) < (fromIndex & BIT_INDEX_MASK) ? /* straddles source words */ ((words[sourceIndex] >>> fromIndex) | (words[sourceIndex+1] & lastWordMask) << -fromIndex) : ((words[sourceIndex] & lastWordMask) >>> fromIndex); // Set wordsInUse correctly result.wordsInUse = targetWords; result.recalculateWordsInUse(); result.checkInvariants(); return result;
public int	hashCode() Returns a hash code value for this bit set. The hash 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, words, 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) < words.length) && ((words[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 = words.length; --i >= 0; ) { h ^= words[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. return a hash code value for this bit set. long h = 1234; for (int i = wordsInUse; --i >= 0; ) h ^= words[i] * (i + 1); return (int)((h >> 32) ^ h);
private void	initWords(int nbits) words = new long[wordIndex(nbits-1) + 1];
public boolean	intersects(java.util.BitSet set) Returns true if the specified BitSet has any bits set to true that are also set to true in this BitSet. param set BitSet to intersect with return boolean indicating whether this BitSet intersects the specified BitSet. since 1.4 for (int i = Math.min(wordsInUse, set.wordsInUse) - 1; i >= 0; i--) if ((words[i] & set.words[i]) != 0) return true; return false;
public boolean	isEmpty() Returns true if this BitSet contains no bits that are set to true. return boolean indicating whether this BitSet is empty. since 1.4 return wordsInUse == 0;
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. return the logical size of this BitSet. since 1.2 if (wordsInUse == 0) return 0; return BITS_PER_WORD * (wordsInUse - 1) + (BITS_PER_WORD - Long.numberOfLeadingZeros(words[wordsInUse - 1]));
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. param fromIndex the index to start checking from (inclusive). return the index of the next clear bit. throws IndexOutOfBoundsException if the specified index is negative. since 1.4 // Neither spec nor implementation handle bitsets of maximal length. // See 4816253. if (fromIndex < 0) throw new IndexOutOfBoundsException("fromIndex < 0: " + fromIndex); checkInvariants(); int u = wordIndex(fromIndex); if (u >= wordsInUse) return fromIndex; long word = ~words[u] & (WORD_MASK << fromIndex); while (true) { if (word != 0) return (u * BITS_PER_WORD) + Long.numberOfTrailingZeros(word); if (++u == wordsInUse) return wordsInUse * BITS_PER_WORD; word = ~words[u]; }
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 } param fromIndex the index to start checking from (inclusive). return the index of the next set bit. throws IndexOutOfBoundsException if the specified index is negative. since 1.4 if (fromIndex < 0) throw new IndexOutOfBoundsException("fromIndex < 0: " + fromIndex); checkInvariants(); int u = wordIndex(fromIndex); if (u >= wordsInUse) return -1; long word = words[u] & (WORD_MASK << fromIndex); while (true) { if (word != 0) return (u * BITS_PER_WORD) + Long.numberOfTrailingZeros(word); if (++u == wordsInUse) return -1; word = words[u]; }
public void	or(java.util.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. param set a bit set. if (this == set) return; int wordsInCommon = Math.min(wordsInUse, set.wordsInUse); if (wordsInUse < set.wordsInUse) { ensureCapacity(set.wordsInUse); wordsInUse = set.wordsInUse; } // Perform logical OR on words in common for (int i = 0; i < wordsInCommon; i++) words[i] |= set.words[i]; // Copy any remaining words if (wordsInCommon < set.wordsInUse) System.arraycopy(set.words, wordsInCommon, words, wordsInCommon, wordsInUse - wordsInCommon); // recalculateWordsInUse() is unnecessary checkInvariants();
private void	readObject(java.io.ObjectInputStream s) Reconstitute the BitSet instance from a stream (i.e., deserialize it). ObjectInputStream.GetField fields = s.readFields(); words = (long[]) fields.get("bits", null); // Assume maximum length then find real length // because recalculateWordsInUse assumes maintenance // or reduction in logical size wordsInUse = words.length; recalculateWordsInUse(); sizeIsSticky = (words.length > 0 && words[words.length-1] == 0L); // heuristic checkInvariants();
private void	recalculateWordsInUse() Set the field wordsInUse with the logical size in words of the bit set. WARNING:This method assumes that the number of words actually in use is less than or equal to the current value of wordsInUse! // Traverse the bitset until a used word is found int i; for (i = wordsInUse-1; i >= 0; i--) if (words[i] != 0) break; wordsInUse = i+1; // The new logical size
public void	set(int bitIndex) Sets the bit at the specified index to true. param bitIndex a bit index. exception IndexOutOfBoundsException if the specified index is negative. since JDK1.0 if (bitIndex < 0) throw new IndexOutOfBoundsException("bitIndex < 0: " + bitIndex); int wordIndex = wordIndex(bitIndex); expandTo(wordIndex); words[wordIndex] |= (1L << bitIndex); // Restores invariants checkInvariants();
public void	set(int bitIndex, boolean value) Sets the bit at the specified index to the specified value. param bitIndex a bit index. param value a boolean value to set. exception IndexOutOfBoundsException if the specified index is negative. since 1.4 if (value) set(bitIndex); else clear(bitIndex);
public void	set(int fromIndex, int toIndex) Sets the bits from the specified fromIndex (inclusive) to the specified toIndex (exclusive) to true. param fromIndex index of the first bit to be set. param toIndex index after the last bit to be set. exception IndexOutOfBoundsException if fromIndex is negative, or toIndex is negative, or fromIndex is larger than toIndex. since 1.4 checkRange(fromIndex, toIndex); if (fromIndex == toIndex) return; // Increase capacity if necessary int startWordIndex = wordIndex(fromIndex); int endWordIndex = wordIndex(toIndex - 1); expandTo(endWordIndex); long firstWordMask = WORD_MASK << fromIndex; long lastWordMask = WORD_MASK >>> -toIndex; if (startWordIndex == endWordIndex) { // Case 1: One word words[startWordIndex] |= (firstWordMask & lastWordMask); } else { // Case 2: Multiple words // Handle first word words[startWordIndex] |= firstWordMask; // Handle intermediate words, if any for (int i = startWordIndex+1; i < endWordIndex; i++) words[i] = WORD_MASK; // Handle last word (restores invariants) words[endWordIndex] |= lastWordMask; } checkInvariants();
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. param fromIndex index of the first bit to be set. param toIndex index after the last bit to be set param value value to set the selected bits to exception IndexOutOfBoundsException if fromIndex is negative, or toIndex is negative, or fromIndex is larger than toIndex. since 1.4 if (value) set(fromIndex, toIndex); else clear(fromIndex, toIndex);
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. return the number of bits currently in this bit set. return words.length * BITS_PER_WORD;
public java.lang.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}". return a string representation of this bit set. checkInvariants(); int numBits = (wordsInUse > 128) ? cardinality() : wordsInUse * BITS_PER_WORD; StringBuilder b = new StringBuilder(6*numBits + 2); b.append('{"); int i = nextSetBit(0); if (i != -1) { b.append(i); for (i = nextSetBit(i+1); i >= 0; i = nextSetBit(i+1)) { int endOfRun = nextClearBit(i); do { b.append(", ").append(i); } while (++i < endOfRun); } } b.append('}"); return b.toString();
private void	trimToSize() Attempts to reduce internal storage used for the bits in this bit set. Calling this method may, but is not required to, affect the value returned by a subsequent call to the {@link #size()} method. if (wordsInUse != words.length) { words = Arrays.copyOf(words, wordsInUse); checkInvariants(); }
private static int	wordIndex(int bitIndex) Given a bit index, return word index containing it. return bitIndex >> ADDRESS_BITS_PER_WORD;
private void	writeObject(java.io.ObjectOutputStream s) Save the state of the BitSet instance to a stream (i.e., serialize it). checkInvariants(); if (! sizeIsSticky) trimToSize(); ObjectOutputStream.PutField fields = s.putFields(); fields.put("bits", words); s.writeFields();
public void	xor(java.util.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. param set a bit set. int wordsInCommon = Math.min(wordsInUse, set.wordsInUse); if (wordsInUse < set.wordsInUse) { ensureCapacity(set.wordsInUse); wordsInUse = set.wordsInUse; } // Perform logical XOR on words in common for (int i = 0; i < wordsInCommon; i++) words[i] ^= set.words[i]; // Copy any remaining words if (wordsInCommon < set.wordsInUse) System.arraycopy(set.words, wordsInCommon, words, wordsInCommon, set.wordsInUse - wordsInCommon); recalculateWordsInUse(); checkInvariants();