java,list转数组

List<String> list = new ArrayList<String>();
if(id != null && !"".equals(id)){
     sb.append( "and tw.id = ? ");
list.add(id);
}
           
if(memo!=null && !"".equals(memo)){
     sb.append( "and tw.memo like ? ");
     list.add("%"+memo+ "%");
}
  sb.append( "order by tw.id desc");
  String[] params = null;
if(list!= null && !list.isEmpty()){
    params= list.toArray(new String[ list.size()]);
}