Tukukkk

This is a really nice Java 8 way to do it:

List<String> list2 = list1.stream().collect(Collectors.toList());

Of course the advantage here is that you can filter and skip to only copy of part of the list.

e.g.

//don't copy the first element 

List<String> list2 = list1.stream().skip(1).collect(Collectors.toList());

I tried to do something like this, but I still got an IndexOutOfBoundsException.

I got a ConcurrentAccessException

This means you are modifying the list while you are trying to copy it, most likely in another thread. To fix this you have to either

• use a collection which is designed for concurrent access.




• lock the collection appropriately so you can iterate over it (or allow you to call a method which does this for you)




• find a away to avoid needing to copy the original list.

originalArrayList.addAll(copyArrayofList);

Please keep on mind whenever using the addAll() method for copy, the contents of both the array lists (originalArrayList and copyArrayofList) references to the same objects will be added to the list so if you modify any one of them then copyArrayofList also will also reflect the same change.

If you don't want side effect then you need to copy each of element from the originalArrayList to the copyArrayofList, like using a for or while loop.

I was having the same problem ConcurrentAccessException and mysolution was to:

List<SomeBean> tempList = new ArrayList<>();



for (CartItem item : prodList) {

  tempList.add(item);

}

prodList.clear();

prodList = new ArrayList<>(tempList);

So it works only one operation at the time and avoids the Exeption...

I tried something similar and was able to reproduce the problem (IndexOutOfBoundsException). Below are my findings:

1) The implementation of the Collections.copy(destList, sourceList) first checks the size of the destination list by calling the size() method. Since the call to the size() method will always return the number of elements in the list (0 in this case), the constructor ArrayList(capacity) ensures only the initial capacity of the backing array and this does not have any relation to the size of the list. Hence we always get IndexOutOfBoundsException.

2) A relatively simple way is to use the constructor that takes a collection as its argument:

List<SomeBean> wsListCopy=new ArrayList<SomeBean>(wsList);  

There is another method with Java 8 in a null-safe way.

List<SomeBean> wsListCopy = Optional.ofNullable(wsList)

                                    .map(List::stream)

                                    .orElseGet(Stream::empty)

                                    .collect(Collectors.toList());

If you want to skip one element.

List<SomeBean> wsListCopy = Optional.ofNullable(wsList)

                                    .map(List::stream)

                                    .orElseGet(Stream::empty)

                                    .skip(1)

                                    .collect(Collectors.toList());

In Java 10:

List<T> newList = List.copyOf(oldList);

List.copyOf() returns an unmodifiable List containing the elements of the given Collection.

 The given Collection must not be null, and it must not contain any null elements.

re: indexOutOfBoundsException, your sublist args are the problem; you need to end the sublist at size-1. Being zero-based, the last element of a list is always size-1, there is no element in the size position, hence the error.

You can use addAll().

eg : wsListCopy.addAll(wsList);

I can't see any correct answer. If you want a deep copy you have to iterate and copy object manually (you could use a copy constructor).

If you do not want changes in one list to effect another list try this.It worked for me
Hope this helps.

  public class MainClass {

  public static void main(String a) {



    List list = new ArrayList();

    list.add("A");



    List list2 = ((List) ((ArrayList) list).clone());



    System.out.println(list);

    System.out.println(list2);



    list.clear();



    System.out.println(list);

    System.out.println(list2);

  }

}



> Output:   

[A]  

[A]  

  

[A]

subList function is a trick, the returned object is still in the original list.
so if you do any operation in subList, it will cause the concurrent exception in your code, no matter it is single thread or multi thread.