code: public StrBuilder insert(int index, Object obj) {
  		if (obj instanceof CharSequence) {
  			return insert(index, (CharSequence) obj);
  		}
  		return insert(index, Convert.toStr(obj));
  	}
docs: 追加对象，对象会被转换为字符串
  
  @param obj 对象
  @return this