Java example source code file (BitSet.java)
The BitSet.java Java example source code
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package java.util;
import java.io.*;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.LongBuffer;
import java.util.stream.IntStream;
import java.util.stream.StreamSupport;
/**
* This class implements a vector of bits that grows as needed. Each
* component of the bit set has a {@code boolean} value. The
* bits of a {@code BitSet} are indexed by nonnegative integers.
* Individual indexed bits can be examined, set, or cleared. One
* {@code BitSet} may be used to modify the contents of another
* {@code BitSet} through logical AND, logical inclusive OR, and
* logical exclusive OR operations.
*
* <p>By default, all bits in the set initially have the value
* {@code false}.
*
* <p>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.
*
* <p>Unless otherwise noted, passing a null parameter to any of the
* methods in a {@code BitSet} will result in a
* {@code NullPointerException}.
*
* <p>A {@code BitSet} is not safe for multithreaded use without
* external synchronization.
*
* @author Arthur van Hoff
* @author Michael McCloskey
* @author Martin Buchholz
* @since JDK1.0
*/
public class BitSet implements Cloneable, java.io.Serializable {
/*
* BitSets are packed into arrays of "words." Currently a word is
* a long, which consists of 64 bits, requiring 6 address bits.
* The choice of word size is determined purely by performance concerns.
*/
private final static int ADDRESS_BITS_PER_WORD = 6;
private final static int BITS_PER_WORD = 1 << ADDRESS_BITS_PER_WORD;
private final static int BIT_INDEX_MASK = BITS_PER_WORD - 1;
/* Used to shift left or right for a partial word mask */
private static final long WORD_MASK = 0xffffffffffffffffL;
/**
* @serialField bits long[]
*
* The bits in this BitSet. The ith bit is stored in bits[i/64] at
* bit position i % 64 (where bit position 0 refers to the least
* significant bit and 63 refers to the most significant bit).
*/
private static final ObjectStreamField[] serialPersistentFields = {
new ObjectStreamField("bits", long[].class),
};
/**
* The internal field corresponding to the serialField "bits".
*/
private long[] words;
/**
* The number of words in the logical size of this BitSet.
*/
private transient int wordsInUse = 0;
/**
* 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 transient boolean sizeIsSticky = false;
/* use serialVersionUID from JDK 1.0.2 for interoperability */
private static final long serialVersionUID = 7997698588986878753L;
/**
* Given a bit index, return word index containing it.
*/
private static int wordIndex(int bitIndex) {
return bitIndex >> ADDRESS_BITS_PER_WORD;
}
/**
* Every public method must preserve these invariants.
*/
private void checkInvariants() {
assert(wordsInUse == 0 || words[wordsInUse - 1] != 0);
assert(wordsInUse >= 0 && wordsInUse <= words.length);
assert(wordsInUse == words.length || words[wordsInUse] == 0);
}
/**
* Sets the field wordsInUse to 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!
*/
private void recalculateWordsInUse() {
// 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
}
/**
* Creates a new bit set. All bits are initially {@code false}.
*/
public BitSet() {
initWords(BITS_PER_WORD);
sizeIsSticky = false;
}
/**
* Creates a bit set whose initial size is large enough to explicitly
* represent bits with indices in the range {@code 0} through
* {@code nbits-1}. All bits are initially {@code false}.
*
* @param nbits the initial size of the bit set
* @throws NegativeArraySizeException if the specified initial size
* is negative
*/
public BitSet(int nbits) {
// nbits can't be negative; size 0 is OK
if (nbits < 0)
throw new NegativeArraySizeException("nbits < 0: " + nbits);
initWords(nbits);
sizeIsSticky = true;
}
private void initWords(int nbits) {
words = new long[wordIndex(nbits-1) + 1];
}
/**
* Creates a bit set using words as the internal representation.
* The last word (if there is one) must be non-zero.
*/
private BitSet(long[] words) {
this.words = words;
this.wordsInUse = words.length;
checkInvariants();
}
/**
* Returns a new bit set containing all the bits in the given long array.
*
* <p>More precisely,
* <br>{@code BitSet.valueOf(longs).get(n) == ((longs[n/64] & (1L<<(n%64))) != 0)}
* <br>for all {@code n < 64 * longs.length}.
*
* <p>This method is equivalent to
* {@code BitSet.valueOf(LongBuffer.wrap(longs))}.
*
* @param 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
* @return a {@code BitSet} containing all the bits in the long array
* @since 1.7
*/
public static BitSet valueOf(long[] longs) {
int n;
for (n = longs.length; n > 0 && longs[n - 1] == 0; n--)
;
return new BitSet(Arrays.copyOf(longs, n));
}
/**
* Returns a new bit set containing all the bits in the given long
* buffer between its position and limit.
*
* <p>More precisely,
* <br>{@code BitSet.valueOf(lb).get(n) == ((lb.get(lb.position()+n/64) & (1L<<(n%64))) != 0)}
* <br>for all {@code n < 64 * lb.remaining()}.
*
* <p>The long buffer is not modified by this method, and no
* reference to the buffer is retained by the bit set.
*
* @param 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
* @return a {@code BitSet} containing all the bits in the buffer in the
* specified range
* @since 1.7
*/
public static BitSet valueOf(LongBuffer lb) {
lb = lb.slice();
int n;
for (n = lb.remaining(); n > 0 && lb.get(n - 1) == 0; n--)
;
long[] words = new long[n];
lb.get(words);
return new BitSet(words);
}
/**
* Returns a new bit set containing all the bits in the given byte array.
*
* <p>More precisely,
* <br>{@code BitSet.valueOf(bytes).get(n) == ((bytes[n/8] & (1<<(n%8))) != 0)}
* <br>for all {@code n < 8 * bytes.length}.
*
* <p>This method is equivalent to
* {@code BitSet.valueOf(ByteBuffer.wrap(bytes))}.
*
* @param 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
* @return a {@code BitSet} containing all the bits in the byte array
* @since 1.7
*/
public static BitSet valueOf(byte[] bytes) {
return BitSet.valueOf(ByteBuffer.wrap(bytes));
}
/**
* Returns a new bit set containing all the bits in the given byte
* buffer between its position and limit.
*
* <p>More precisely,
* <br>{@code BitSet.valueOf(bb).get(n) == ((bb.get(bb.position()+n/8) & (1<<(n%8))) != 0)}
* <br>for all {@code n < 8 * bb.remaining()}.
*
* <p>The byte buffer is not modified by this method, and no
* reference to the buffer is retained by the bit set.
*
* @param 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
* @return a {@code BitSet} containing all the bits in the buffer in the
* specified range
* @since 1.7
*/
public static BitSet valueOf(ByteBuffer bb) {
bb = bb.slice().order(ByteOrder.LITTLE_ENDIAN);
int n;
for (n = bb.remaining(); n > 0 && bb.get(n - 1) == 0; n--)
;
long[] words = new long[(n + 7) / 8];
bb.limit(n);
int i = 0;
while (bb.remaining() >= 8)
words[i++] = bb.getLong();
for (int remaining = bb.remaining(), j = 0; j < remaining; j++)
words[i] |= (bb.get() & 0xffL) << (8 * j);
return new BitSet(words);
}
/**
* Returns a new byte array containing all the bits in this bit set.
*
* <p>More precisely, if
* <br>{@code byte[] bytes = s.toByteArray();}
* <br>then {@code bytes.length == (s.length()+7)/8} and
* <br>{@code s.get(n) == ((bytes[n/8] & (1<<(n%8))) != 0)}
* <br>for all {@code n < 8 * bytes.length}.
*
* @return a byte array containing a little-endian representation
* of all the bits in this bit set
* @since 1.7
*/
public byte[] toByteArray() {
int n = wordsInUse;
if (n == 0)
return new byte[0];
int len = 8 * (n-1);
for (long x = words[n - 1]; x != 0; x >>>= 8)
len++;
byte[] bytes = new byte[len];
ByteBuffer bb = ByteBuffer.wrap(bytes).order(ByteOrder.LITTLE_ENDIAN);
for (int i = 0; i < n - 1; i++)
bb.putLong(words[i]);
for (long x = words[n - 1]; x != 0; x >>>= 8)
bb.put((byte) (x & 0xff));
return bytes;
}
/**
* Returns a new long array containing all the bits in this bit set.
*
* <p>More precisely, if
* <br>{@code long[] longs = s.toLongArray();}
* <br>then {@code longs.length == (s.length()+63)/64} and
* <br>{@code s.get(n) == ((longs[n/64] & (1L<<(n%64))) != 0)}
* <br>for all {@code n < 64 * longs.length}.
*
* @return a long array containing a little-endian representation
* of all the bits in this bit set
* @since 1.7
*/
public long[] toLongArray() {
return Arrays.copyOf(words, wordsInUse);
}
/**
* Ensures that the BitSet can hold enough words.
* @param wordsRequired the minimum acceptable number of words.
*/
private void ensureCapacity(int wordsRequired) {
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;
}
}
/**
* 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.
*/
private void expandTo(int wordIndex) {
int wordsRequired = wordIndex+1;
if (wordsInUse < wordsRequired) {
ensureCapacity(wordsRequired);
wordsInUse = wordsRequired;
}
}
/**
* Checks that fromIndex ... toIndex is a valid range of bit indices.
*/
private static void checkRange(int fromIndex, int toIndex) {
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);
}
/**
* Sets the bit at the specified index to the complement of its
* current value.
*
* @param bitIndex the index of the bit to flip
* @throws IndexOutOfBoundsException if the specified index is negative
* @since 1.4
*/
public void flip(int bitIndex) {
if (bitIndex < 0)
throw new IndexOutOfBoundsException("bitIndex < 0: " + bitIndex);
int wordIndex = wordIndex(bitIndex);
expandTo(wordIndex);
words[wordIndex] ^= (1L << bitIndex);
recalculateWordsInUse();
checkInvariants();
}
/**
* Sets each bit from the specified {@code fromIndex} (inclusive) to the
* specified {@code 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
* @throws IndexOutOfBoundsException if {@code fromIndex} is negative,
* or {@code toIndex} is negative, or {@code fromIndex} is
* larger than {@code toIndex}
* @since 1.4
*/
public void flip(int fromIndex, int toIndex) {
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();
}
/**
* Sets the bit at the specified index to {@code true}.
*
* @param bitIndex a bit index
* @throws IndexOutOfBoundsException if the specified index is negative
* @since JDK1.0
*/
public void set(int bitIndex) {
if (bitIndex < 0)
throw new IndexOutOfBoundsException("bitIndex < 0: " + bitIndex);
int wordIndex = wordIndex(bitIndex);
expandTo(wordIndex);
words[wordIndex] |= (1L << bitIndex); // Restores invariants
checkInvariants();
}
/**
* Sets the bit at the specified index to the specified value.
*
* @param bitIndex a bit index
* @param value a boolean value to set
* @throws IndexOutOfBoundsException if the specified index is negative
* @since 1.4
*/
public void set(int bitIndex, boolean value) {
if (value)
set(bitIndex);
else
clear(bitIndex);
}
/**
* Sets the bits from the specified {@code fromIndex} (inclusive) to the
* specified {@code toIndex} (exclusive) to {@code true}.
*
* @param fromIndex index of the first bit to be set
* @param toIndex index after the last bit to be set
* @throws IndexOutOfBoundsException if {@code fromIndex} is negative,
* or {@code toIndex} is negative, or {@code fromIndex} is
* larger than {@code toIndex}
* @since 1.4
*/
public void set(int fromIndex, int toIndex) {
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();
}
/**
* Sets the bits from the specified {@code fromIndex} (inclusive) to the
* specified {@code 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
* @throws IndexOutOfBoundsException if {@code fromIndex} is negative,
* or {@code toIndex} is negative, or {@code fromIndex} is
* larger than {@code toIndex}
* @since 1.4
*/
public void set(int fromIndex, int toIndex, boolean value) {
if (value)
set(fromIndex, toIndex);
else
clear(fromIndex, toIndex);
}
/**
* Sets the bit specified by the index to {@code false}.
*
* @param bitIndex the index of the bit to be cleared
* @throws IndexOutOfBoundsException if the specified index is negative
* @since JDK1.0
*/
public void clear(int bitIndex) {
if (bitIndex < 0)
throw new IndexOutOfBoundsException("bitIndex < 0: " + bitIndex);
int wordIndex = wordIndex(bitIndex);
if (wordIndex >= wordsInUse)
return;
words[wordIndex] &= ~(1L << bitIndex);
recalculateWordsInUse();
checkInvariants();
}
/**
* Sets the bits from the specified {@code fromIndex} (inclusive) to the
* specified {@code toIndex} (exclusive) to {@code false}.
*
* @param fromIndex index of the first bit to be cleared
* @param toIndex index after the last bit to be cleared
* @throws IndexOutOfBoundsException if {@code fromIndex} is negative,
* or {@code toIndex} is negative, or {@code fromIndex} is
* larger than {@code toIndex}
* @since 1.4
*/
public void clear(int fromIndex, int toIndex) {
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();
}
/**
* Sets all of the bits in this BitSet to {@code false}.
*
* @since 1.4
*/
public void clear() {
while (wordsInUse > 0)
words[--wordsInUse] = 0;
}
/**
* Returns the value of the bit with the specified index. The value
* is {@code true} if the bit with the index {@code bitIndex}
* is currently set in this {@code BitSet}; otherwise, the result
* is {@code false}.
*
* @param bitIndex the bit index
* @return the value of the bit with the specified index
* @throws IndexOutOfBoundsException if the specified index is negative
*/
public boolean get(int bitIndex) {
if (bitIndex < 0)
throw new IndexOutOfBoundsException("bitIndex < 0: " + bitIndex);
checkInvariants();
int wordIndex = wordIndex(bitIndex);
return (wordIndex < wordsInUse)
&& ((words[wordIndex] & (1L << bitIndex)) != 0);
}
/**
* Returns a new {@code BitSet} composed of bits from this {@code BitSet}
* from {@code fromIndex} (inclusive) to {@code toIndex} (exclusive).
*
* @param fromIndex index of the first bit to include
* @param toIndex index after the last bit to include
* @return a new {@code BitSet} from a range of this {@code BitSet}
* @throws IndexOutOfBoundsException if {@code fromIndex} is negative,
* or {@code toIndex} is negative, or {@code fromIndex} is
* larger than {@code toIndex}
* @since 1.4
*/
public BitSet get(int fromIndex, int toIndex) {
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;
}
/**
* Returns the index of the first bit that is set to {@code true}
* that occurs on or after the specified starting index. If no such
* bit exists then {@code -1} is returned.
*
* <p>To iterate over the {@code true} bits in a {@code BitSet},
* use the following loop:
*
* <pre> {@code
* for (int i = bs.nextSetBit(0); i >= 0; i = bs.nextSetBit(i+1)) {
* // operate on index i here
* }}</pre>
*
* @param fromIndex the index to start checking from (inclusive)
* @return the index of the next set bit, or {@code -1} if there
* is no such bit
* @throws IndexOutOfBoundsException if the specified index is negative
* @since 1.4
*/
public int nextSetBit(int fromIndex) {
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];
}
}
/**
* Returns the index of the first bit that is set to {@code 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
*/
public int nextClearBit(int fromIndex) {
// 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];
}
}
/**
* Returns the index of the nearest bit that is set to {@code true}
* that occurs on or before the specified starting index.
* If no such bit exists, or if {@code -1} is given as the
* starting index, then {@code -1} is returned.
*
* <p>To iterate over the {@code true} bits in a {@code BitSet},
* use the following loop:
*
* <pre> {@code
* for (int i = bs.length(); (i = bs.previousSetBit(i-1)) >= 0; ) {
* // operate on index i here
* }}</pre>
*
* @param fromIndex the index to start checking from (inclusive)
* @return the index of the previous set bit, or {@code -1} if there
* is no such bit
* @throws IndexOutOfBoundsException if the specified index is less
* than {@code -1}
* @since 1.7
*/
public int previousSetBit(int fromIndex) {
if (fromIndex < 0) {
if (fromIndex == -1)
return -1;
throw new IndexOutOfBoundsException(
"fromIndex < -1: " + fromIndex);
}
checkInvariants();
int u = wordIndex(fromIndex);
if (u >= wordsInUse)
return length() - 1;
long word = words[u] & (WORD_MASK >>> -(fromIndex+1));
while (true) {
if (word != 0)
return (u+1) * BITS_PER_WORD - 1 - Long.numberOfLeadingZeros(word);
if (u-- == 0)
return -1;
word = words[u];
}
}
/**
* Returns the index of the nearest bit that is set to {@code false}
* that occurs on or before the specified starting index.
* If no such bit exists, or if {@code -1} is given as the
* starting index, then {@code -1} is returned.
*
* @param fromIndex the index to start checking from (inclusive)
* @return the index of the previous clear bit, or {@code -1} if there
* is no such bit
* @throws IndexOutOfBoundsException if the specified index is less
* than {@code -1}
* @since 1.7
*/
public int previousClearBit(int fromIndex) {
if (fromIndex < 0) {
if (fromIndex == -1)
return -1;
throw new IndexOutOfBoundsException(
"fromIndex < -1: " + fromIndex);
}
checkInvariants();
int u = wordIndex(fromIndex);
if (u >= wordsInUse)
return fromIndex;
long word = ~words[u] & (WORD_MASK >>> -(fromIndex+1));
while (true) {
if (word != 0)
return (u+1) * BITS_PER_WORD -1 - Long.numberOfLeadingZeros(word);
if (u-- == 0)
return -1;
word = ~words[u];
}
}
/**
* Returns the "logical size" of this {@code BitSet}: the index of
* the highest set bit in the {@code BitSet} plus one. Returns zero
* if the {@code BitSet} contains no set bits.
*
* @return the logical size of this {@code BitSet}
* @since 1.2
*/
public int length() {
if (wordsInUse == 0)
return 0;
return BITS_PER_WORD * (wordsInUse - 1) +
(BITS_PER_WORD - Long.numberOfLeadingZeros(words[wordsInUse - 1]));
}
/**
* Returns true if this {@code BitSet} contains no bits that are set
* to {@code true}.
*
* @return boolean indicating whether this {@code BitSet} is empty
* @since 1.4
*/
public boolean isEmpty() {
return wordsInUse == 0;
}
/**
* Returns true if the specified {@code BitSet} has any bits set to
* {@code true} that are also set to {@code true} in this {@code BitSet}.
*
* @param set {@code BitSet} to intersect with
* @return boolean indicating whether this {@code BitSet} intersects
* the specified {@code BitSet}
* @since 1.4
*/
public boolean intersects(BitSet set) {
for (int i = Math.min(wordsInUse, set.wordsInUse) - 1; i >= 0; i--)
if ((words[i] & set.words[i]) != 0)
return true;
return false;
}
/**
* Returns the number of bits set to {@code true} in this {@code BitSet}.
*
* @return the number of bits set to {@code true} in this {@code BitSet}
* @since 1.4
*/
public int cardinality() {
int sum = 0;
for (int i = 0; i < wordsInUse; i++)
sum += Long.bitCount(words[i]);
return sum;
}
/**
* Performs a logical <b>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 {@code true} if and only if it both initially
* had the value {@code true} and the corresponding bit in the
* bit set argument also had the value {@code true}.
*
* @param set a bit set
*/
public void and(BitSet 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();
}
/**
* Performs a logical <b>OR of this bit set with the bit set
* argument. This bit set is modified so that a bit in it has the
* value {@code true} if and only if it either already had the
* value {@code true} or the corresponding bit in the bit set
* argument has the value {@code true}.
*
* @param set a bit set
*/
public void or(BitSet 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();
}
/**
* Performs a logical <b>XOR of this bit set with the bit set
* argument. This bit set is modified so that a bit in it has the
* value {@code true} if and only if one of the following
* statements holds:
* <ul>
* <li>The bit initially has the value {@code true}, and the
* corresponding bit in the argument has the value {@code false}.
* <li>The bit initially has the value {@code false}, and the
* corresponding bit in the argument has the value {@code true}.
* </ul>
*
* @param set a bit set
*/
public void xor(BitSet 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();
}
/**
* Clears all of the bits in this {@code BitSet} whose corresponding
* bit is set in the specified {@code BitSet}.
*
* @param set the {@code BitSet} with which to mask this
* {@code BitSet}
* @since 1.2
*/
public void andNot(BitSet set) {
// 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();
}
/**
* Returns the hash code value for this bit set. The hash code depends
* only on which bits are set within this {@code BitSet}.
*
* <p>The hash code is defined to be the result of the following
* calculation:
* <pre> {@code
* 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);
* }}</pre>
* Note that the hash code changes if the set of bits is altered.
*
* @return the hash code value for this bit set
*/
public int hashCode() {
long h = 1234;
for (int i = wordsInUse; --i >= 0; )
h ^= words[i] * (i + 1);
return (int)((h >> 32) ^ h);
}
/**
* Returns the number of bits of space actually in use by this
* {@code 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
*/
public int size() {
return words.length * BITS_PER_WORD;
}
/**
* Compares this object against the specified object.
* The result is {@code true} if and only if the argument is
* not {@code null} and is a {@code Bitset} object that has
* exactly the same set of bits set to {@code true} as this bit
* set. That is, for every nonnegative {@code int} index {@code k},
* <pre>((BitSet)obj).get(k) == this.get(k)
* must be true. The current sizes of the two bit sets are not compared.
*
* @param obj the object to compare with
* @return {@code true} if the objects are the same;
* {@code false} otherwise
* @see #size()
*/
public boolean equals(Object obj) {
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;
}
/**
* Cloning this {@code BitSet} produces a new {@code BitSet}
* that is equal to it.
* The clone of the bit set is another bit set that has exactly the
* same bits set to {@code true} as this bit set.
*
* @return a clone of this bit set
* @see #size()
*/
public Object clone() {
if (! sizeIsSticky)
trimToSize();
try {
BitSet result = (BitSet) super.clone();
result.words = words.clone();
result.checkInvariants();
return result;
} catch (CloneNotSupportedException e) {
throw new InternalError(e);
}
}
/**
* 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.
*/
private void trimToSize() {
if (wordsInUse != words.length) {
words = Arrays.copyOf(words, wordsInUse);
checkInvariants();
}
}
/**
* Save the state of the {@code BitSet} instance to a stream (i.e.,
* serialize it).
*/
private void writeObject(ObjectOutputStream s)
throws IOException {
checkInvariants();
if (! sizeIsSticky)
trimToSize();
ObjectOutputStream.PutField fields = s.putFields();
fields.put("bits", words);
s.writeFields();
}
/**
* Reconstitute the {@code BitSet} instance from a stream (i.e.,
* deserialize it).
*/
private void readObject(ObjectInputStream s)
throws IOException, ClassNotFoundException {
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();
}
/**
* Returns a string representation of this bit set. For every index
* for which this {@code 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.
*
* <p>Example:
* <pre>
* BitSet drPepper = new BitSet();</pre>
* Now {@code drPepper.toString()} returns "{@code {}}".
* <pre>
* drPepper.set(2);</pre>
* Now {@code drPepper.toString()} returns "{@code {2}}".
* <pre>
* drPepper.set(4);
* drPepper.set(10);</pre>
* Now {@code drPepper.toString()} returns "{@code {2, 4, 10}}".
*
* @return a string representation of this bit set
*/
public String toString() {
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();
}
/**
* Returns a stream of indices for which this {@code 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 {@link #cardinality()} method.
*
* <p>The bit set must remain constant during the execution of the
* terminal stream operation. Otherwise, the result of the terminal
* stream operation is undefined.
*
* @return a stream of integers representing set indices
* @since 1.8
*/
public IntStream stream() {
class BitSetIterator implements PrimitiveIterator.OfInt {
int next = nextSetBit(0);
@Override
public boolean hasNext() {
return next != -1;
}
@Override
public int nextInt() {
if (next != -1) {
int ret = next;
next = nextSetBit(next+1);
return ret;
} else {
throw new NoSuchElementException();
}
}
}
return StreamSupport.intStream(
() -> Spliterators.spliterator(
new BitSetIterator(), cardinality(),
Spliterator.ORDERED | Spliterator.DISTINCT | Spliterator.SORTED),
Spliterator.SIZED | Spliterator.SUBSIZED |
Spliterator.ORDERED | Spliterator.DISTINCT | Spliterator.SORTED,
false);
}
}
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