BitSet flip（）是否会影响BitSet的长度？

Question

In the following function, I would like to mutate a BitSet based on a mutation probability.

public static Cell mutate(Cell original_){

    Double mProb = 0.2;

    BitSet original = new BitSet(original_.getChrom().size());

    original = (BitSet) original_.getChrom().clone();

    Random rand = new Random();
    System.out.print(" " + original.length() + " "); //to check the length of original before applying flip()

    for(int m = 0; m < original.length(); m++)
    {

        if(rand.nextDouble() <= mProb){
            original.flip(m);
        }

    }

    System.out.print(" " + original.length() + " "); //to check the length of original after applying flip()

    Cell mutated = new Cell(original);
    //System.out.print("{" + mutated.getFitness() + "} ");

    return mutated;
}

The problem that I noticed is that sometimes the length of BitSet is reduced after flipping some bits!!

The following some results to explain the problem:

original before flip || length before flip || original after flip || length after flip
110111               || 6                  || 110111              || 6
101111               || 6                  || 111                 || 3
110111               || 6                  || 10111               || 5
110111               || 6                  || 111111              || 6
111010               || 6                  || 11010               || 5

As you can see, the first and the fourth weren't reduced after flipping. While the other have been reduced. I tried to understand what caused the problem but I couldn't. All what I need is that after the flipping the bitset should have the same length as the original before flipping.

Answer 1

Does BitSet flip() affect the length of BitSet?

Yes

Javadoc for BitSet::length says:

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.

BitSet b = new BitSet();
System.out.println(b.length()); // 0
b.flip(1);
System.out.println(b.length()); // 2
b.flip(1);
System.out.println(b.length()); // 0