在 ArrayList 中插入时出现 java.util.ConcurrentModificationException

Question

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Answer 1

发生这种情况是因为在创建Iterator 之后修改了数组列表。

The iterators returned by this ArrayList's iterator and listIterator methods are fail-fast: if the list is structurally modified at any time after the iterator is created, in any way except through the iterator's own remove or add methods, the iterator will throw a ConcurrentModificationException. Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.

Documentation

Iterator<String> lir = al.iterator(); // Iterator created

while (lir.hasNext()) 
    System.out.println(lir.next());
al.add(2, "inserted"); // List is modified here
while (lir.hasNext()) 
    System.out.println(lir.next());// Again it try to access list 

你在这里应该做的是在修改后创建新的迭代器对象。

...
al.add(2, "inserted");
lir = al.iterator();
while (lir.hasNext()) 
    System.out.println(lir.next());