public FlatBufferBuilder(int initial_size){
  if (initial_size <= 0)   initial_size=1;
  space=initial_size;
  bb=newByteBuffer(initial_size);
}

public FlatBufferBuilder ( int initial_size ) { if ( initial_size <= 0 ) initial_size = 1 ; space = initial_size ; bb = newByteBuffer ( initial_size ) ; }
start with a buffer of size ` initial_size ` , then grow as required .
