java while(LinkedList.iterator().hasNext())不起作用

Question

我有以下while循环,如果我在while循环条件中放入this.boatTripsList.iterator().hasNext(),则抛出错误.当我创建迭代器然后放入while循环条件时,它将工作.为什么是这样？感谢和问候.(第二个版本抛出错误)

 public Journey(List<BoatTrip> trips) {
   this.boatTripsList = new LinkedList<BoatTrip>();
   Iterator<BoatTrip> iterator = trips.iterator();
   //add the given boat trips to the boattrips list
    while (iterator.hasNext()) {
         BoatTrip thistrip = iterator.next();
         this.boatTripsList.add(thistrip);
    }
}



public Journey(List<BoatTrip> trips) {
   this.boatTripsList = new LinkedList<BoatTrip>();
   //add the given boat trips to the boattrips list
    while (trips.iterator().hasNext()) {
         BoatTrip thistrip = iterator.next();
         this.boatTripsList.add(thistrip);
    }
}

Answer 1

这是正常的:如果您的while条件是while(trips.iterator().hasNext()),则每次都创建一个新的迭代器.如果您的列表不为空,那么条件将始终为真......

在循环本身中,你使用你在进入循环之前创建的迭代器...结果,NoSuchElementException当这个迭代器为空时你会得到一个.

使用:

final Iterator<Whatever> = list.iterator();
Whatever whatever;

while (iterator.hasNext()) {
     whatever = iterator.next();
     // do whatever stuff
}

但对于步行列表,首选的是foreach循环:

for (final BoatTrip trip: tripList)
    // do whatever is needed

如果要将列表的内容添加到另一个列表,请使用.addAll():

// no need for the "this" qualifier, there is no name conflict
boatTripList.addAll(trips);