Java: Count number of bits set in a java.util.BitSet

Question

Any quick method to count the number of set bits in a BitSet other than the usual 'keep a counter' method?

Answer 1

The cardinality() method returns the number of set bits.

Answer 2

(Assuming you don't want to call cardinality())

int count = 0; 
for (int i = bs.nextSetBit(0); i >= 0; i = bs.nextSetBit(i+1)) {
    count++;
}

see javadoc

Answer 3

BitSet B1 = new BitSet(3);
B1.set(0);
B1.cardinality();

Output:

1