ArrayIndexOutOfBoundsException when using the ArrayList s iterator

Question

Right now  I have a program containing a piece of code that looks like this   while  arrayList iterator   hasNext             value is equal to a String value      if  arrayList iterator   next   equals value                  do something             Am I doing that right  as far as iterating through the ArrayList goes   The error I am getting is   java lang ArrayIndexOutOfBoundsException  -1     at java util ArrayList get Unknown Source      at main1 endElement main1 java 244      at com sun org apache xerces internal parsers AbstractSAXParser endElement Unknown Source      at com sun org apache xerces internal impl XMLDocumentFragmentScannerImpl scanEndElement Unknown Source      at com sun org apache xerces internal impl XMLDocumentFragmentScannerImpl FragmentContentDriver next Unknown Source      at com sun org apache xerces internal impl XMLDocumentScannerImpl next Unknown Source      at com sun org apache xerces internal impl XMLDocumentFragmentScannerImpl scanDocument Unknown Source      at com sun org apache xerces internal parsers XML11Configuration parse Unknown Source      at com sun org apache xerces internal parsers XML11Configuration parse Unknown Source      at com sun org apache xerces internal parsers XMLParser parse Unknown Source      at com sun org apache xerces internal parsers AbstractSAXParser parse Unknown Source      at com sun org apache xerces internal jaxp SAXParserImpl JAXPSAXParser parse Unknown Source      at javax xml parsers SAXParser parse Unknown Source      at javax xml parsers SAXParser parse Unknown Source      at main1 traverse main1 java 73      at main1 traverse main1 java 102      at main1 traverse main1 java 102      at main1 main main1 java 404    I would show the rest of the code  but it s pretty extensive  and if I am not doing the iteration correctly  I would assume the only possibility is that I am not initializing the ArrayList properly

User · Answer

You could also do a for loop as you would for an array but instead of array i  you would use list get i   for  int i   0  i  lt  list size    i          System out println list get i

User · Answer

List lt String gt  arrayList   new ArrayList lt String gt     for  String s   arrayList        if s equals value              do something           or  for  int i   0  i  lt  arrayList size    i          if arrayList get i  equals value              do something           But be carefull ArrayList can hold null values  So comparation should be  value equals arrayList get i     when you are sure that value is not null or you should check if given element is null

User · Answer

iterating using iterator is not fail-safe for example if you add element to the collection after iterator s creation then it will throw concurrentmodificaionexception  Also it s not thread safe  you have to make it thread safe externally   So it s better to use for-each structure of for loop  It s atleast fail-safe

User · Answer

While I agree that the accepted answer is usually the best solution and definitely easier to use  I noticed no one displayed the proper usage of the iterator  So here is a quick example   Iterator lt Object gt  it   arrayList iterator    while it hasNext          Object obj   it next          Do something with obj

User · Answer

Efficient way to iterate your ArrayList followed by this link  This type will improve the performance of looping during iteration  int size   list size     for int j   0  j  lt  size  j          System out println list get i

User · Answer

Apart of larsmans answer  who is indeed correct   the exception in a call to a get   method  so the code you have posted is not the one that is causing the error

User · Answer

Am I doing that right  as far as iterating through the Arraylist goes    No  by calling iterator twice in each iteration  you re getting new iterators all the time   The easiest way to write this loop is using the for-each construct   for  String s   arrayList      if  s equals value                    As for     java lang ArrayIndexOutOfBoundsException  -1   You just tried to get element number -1 from an array  Counting starts at zero

User · Answer

You can also use like this   for Iterator iterator   arrayList iterator    iterator hasNext       x   iterator next      do some stuff     Its a good practice to cast and use the object  For example  if the  arrayList  contains a list of  Object1  objects  Then  we can re-write the code as   for Iterator iterator   arrayList iterator    iterator hasNext       x    Object1  iterator next      do some stuff

[java] ArrayIndexOutOfBoundsException when using the ArrayList's iterator

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