private void print(int d) {
      StringBuilder buf = new StringBuilder();
      buf.append("NBSI - _bits.len=");
      NBSI x = this;
      while( x != null ) {
        buf.append(" "+x._bits.length);
        x = x._nbsi64;
      }
      print(d,buf.toString());

      x = this;
      while( x != null ) {
        for( int i=0; i<x._bits.length; i++ )
          System.out.print(Long.toHexString(x._bits[i])+" ");
        x = x._nbsi64;
        System.out.println();
      }

      if( _copyIdx.get() != 0 || _copyDone.get() != 0 )
        print(d,"_copyIdx="+_copyIdx.get()+" _copyDone="+_copyDone.get()+" _words_to_cpy="+_sum_bits_length);
      if( _new != null ) {
        print(d,"__has_new - ");
        _new.print(d+1);
      }
    }
Standard Java {@link Iterator}.  Not very efficient because it
auto-boxes the returned values.
jctools-core/src/main/java/org/jctools/maps/NonBlockingSetInt.java