List String to ArrayList String conversion issue

Question

I have a following method   which actually takes the list of sentences and splits each sentence into words  Here is it   public List lt String gt  getWords List lt String gt  strSentences   allWords   new ArrayList lt String gt         Iterator lt String gt  itrTemp   strSentences iterator        while itrTemp hasNext             String strTemp   itrTemp next            allWords   Arrays asList strTemp toLowerCase   split    s                          return allWords      I have to pass this list into a hashmap in a following format       HashMap lt String  ArrayList lt String gt  gt    so this method returns List and I need a arrayList  If I try to cast it doesn t workout    any suggestions   Also  if I change the ArrayList to List in a HashMap  I get         java lang UnsupportedOperationException   because of this line in my code   sentenceList add   Element sentenceNodeList item sentenceIndex   getTextContent       Any better suggestions

User · Accepted Answer

First of all  why is the map a HashMap lt String  ArrayList lt String gt  gt  and not a HashMap lt String  List lt String gt  gt   Is there some reason why the value must be a specific implementation of interface List  ArrayList in this case    Arrays asList does not return a java util ArrayList  so you can t assign the return value of Arrays asList to a variable of type ArrayList   Instead of   allWords   Arrays asList strTemp toLowerCase   split    s        Try this   allWords addAll Arrays asList strTemp toLowerCase   split    s

User · Answer

Take a look at ArrayList addAll Collection      Appends all of the elements in the specified collection to the end of   this list  in the order that they are returned by the specified   collection s Iterator  The behaviour of this operation is undefined if   the specified collection is modified while the operation is in   progress   This implies that the behaviour of this call is undefined if   the specified collection is this list  and this list is nonempty     So basically you could use  ArrayList lt String gt  listOfStrings   new ArrayList lt  gt  list size     listOfStrings addAll list

User · Answer

In Kotlin List can be converted into ArrayList through passing it as a constructor parameter   ArrayList list

User · Answer

Tried and tested approach    public static ArrayList lt String gt  listToArrayList List lt Object gt  myList            ArrayList lt String gt  arl   new ArrayList lt String gt             for  Object object   myList                arl add  String  object                     return arl

User · Answer

Cast works where the actual instance of the list is an ArrayList  If it is  say  a Vector  which is another extension of List  it will throw a ClassCastException   The error when changing the definition of your HashMap is due to the elements later being processed  and that process expects a method that is defined only in ArrayList  The exception tells you that it did not found the method it was looking for   Create a new ArrayList with the contents of the old one   new ArrayList lt String gt  myList

User · Answer

Arrays asList does not return instance of java util ArrayListbut it returns instance of java util Arrays ArrayList    You will need to convert to ArrayList if you want to access ArrayList specific information  allWords addAll Arrays asList strTemp toLowerCase   split    s

[java] List<String> to ArrayList<String> conversion issue

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