What do Bitset size() and length() mean, and what is the difference between them?

I don’t quite understand the different meanings of size() and length() in BitSet. Check the code below:

public class Sandbox {

   public static void main(String argv[]) 
   {
       BitSet bitSet1 = new BitSet(16);
       bitSet1.set(0);
       bitSet1.set(8);
       bitSet1.set(15);
       displayBitSet(bitSet1);
       
    
 
   }
   
   static void displayBitSet(BitSet bitSet)
   {
       for(int i=0;i<bitSet.size();i++)
       {
           boolean bit = bitSet.get(i);
           System.out.print(bit?1:0);
       }
       System.out.println(" "+bitSet.size()+" "+bitSet.length());
   }
 
}

Output is:

1000000010000001000000000000000000000000000000000000000000000000 64 16

I thought I would get something like

1000000010000001 16 16

Where do these trailing zeroes come from? Can someone explain this to me? thanks~~

Answer

answer is quite simple the BitSet constructor just says it generates something which is big enough to the given size, actually it takes some internal size which is best matching.

And in your case this is 64 bit, see JavaDoc