小编Sac*_*Gax的帖子

vector<string> frame(const vector<string>& v){
   vector<string> ret;
   string::size_type maxlen = width(v);
   string border(maxlen + 4,'*');

   //write the top border
   ret.push_back(border);

  //write each interior row
  for(vector<string>::const_iterator i = v.begin();i != v.end();++i){
     ret.push_back("* " + *i + string(maxlen- (*i.size()),' ') + " *");
  }

  //write the bottom border
  ret.push_back(border);

  return ret;
 }

在for循环中,我在访问迭代器返回的字符串的size()成员函数时遇到错误i ---->*i.size();

"class"std :: _ Vector_const_iterator >>"没有成员"大小"

我在以下代码中收到 NullPointerException ：

private Map<String,List<Entry>> Days;
private void intializeDays() {
    //Iterate over the DayOfWeek enum and put the keys in Map
    for(DayOfWeek dw : EnumSet.range(DayOfWeek.MONDAY,DayOfWeek.SUNDAY)){
    List<Entry> entries = null;
    Days.put(dw.toString().toLowerCase(),entries);
    }
}

我认为是因为

List<Entry> entries = null;

但是如何创建一个空列表并将其添加到地图中？

是什么[1]在声明中到底意味着什么？

String magnitudeString = details.split(" ")[1];

不能这样写:

String [] magnitudeString = details.split(" ");