在TreeSet上使用迭代器 [英] Using iterator on a TreeSet

问题描述

情况：我有一个TreeSet的自定义对象，我也使用了自定义比较器。我已经创建了一个迭代器在这个TreeSet上使用。

  TreeSet< Custom> ts = new TreeSet< Custom>（）; 
迭代器< Custom> itr = ts.iterator（）; 
 while（itr.hasNext（））{
 Custom c = itr.next（）; 
 //为TreeSet添加新元素的代码ts 
} 
  

问题：我想知道，如果我在while循环中向TreeSet添加一个新元素，那么该新元素将立即排序。换句话说，如果我在while循环中添加一个新元素，并且它小于我当前在c中保存的元素，那么在下一次迭代中，我将在c中获得与上一次迭代中相同的元素？因为在排序之后，新添加的元素将占据当前元素之前的某个位置。）

解决方案

你的迭代，你的下一个迭代器调用可能会抛出一个 ConcurrentModificationException 。请参见 TreeSet 文档中的快速故障行为。 p>

要迭代和添加元素，您可以先复制到另一个集合：

  TreeSet< Custom> ts = ... 
 TreeSet< Custom> tsWithExtra = new TreeSet（ts）; 
 
 for（Custom c：ts）{
 //可能添加到tsWithExtra 
} 
 
 //继续使用tsWithExtra 
  

或创建单独的集合以在迭代后与 ts 正如Colin建议的那样。

SITUATION: I have a TreeSet of custom Objects and I have also used a custom Comparator. I have created an iterator to use on this TreeSet.

TreeSet<Custom> ts=new TreeSet<Custom>();
Iterator<Custom> itr=ts.iterator();
while(itr.hasNext()){
    Custom c=itr.next();
    //Code to add a new element to the TreeSet ts
}

QUESTION: Well I want to know that if I add a new element to the TreeSet within the while loop, then will that new element get sorted immediately. In other words, if I add a new element within the while loop and it is less than the one which I am currently holding in c, then in the next iteration will I be getting the same element in c as in the last iteration?(since after sorting, the newly added element will occupy a place somewhere before the current element).

解决方案

If you add an element during your iteration, your next iterator call will likely throw a ConcurrentModificationException. See the fail-fast behavior in TreeSet docs.

To iterate and add elements, you could copy first to another set:

TreeSet<Custom> ts = ...
TreeSet<Custom> tsWithExtra = new TreeSet(ts);

for (Custom c : ts) {
  // possibly add to tsWithExtra
}

// continue, using tsWithExtra

or create a separate collection to be merged with ts after iteration, as Colin suggests.

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