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How to avoid java.util.ConcurrentModificationException when iterating through and removing elements from an ArrayList16个
import java.util.ArrayList; import java.util.Iterator; import java.util.ListIterator; public class MyList { public static void main(String[] args) { ArrayList<String> al = new ArrayList<String>(); al.add("S1"); al.add("S2"); al.add("S3"); al.add("S4"); Iterator<String> lir = al.iterator(); while (lir.hasNext()) { System.out.println(lir.next()); } al.add(2,"inserted"); while (lir.hasNext()) { System.out.println(lir.next()); } } }
Exception in thread "main" java.util.ConcurrentModificationException at java.util.ArrayList$Itr.checkForComodification(Unknown Source) at java.util.ArrayList$Itr.next(Unknown Source) at collections.MyList.main(MyList.java:32)
解决方法
这是因为在创建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.
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
你应该在这里做什么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());