java - How to sort CopyOnWriteArrayList

Question

I want to sort CopyOnWriteArrayList. But when I tried to run the following code

It is throwing unsorted operation exception.

public class CopyOnWriteArrayListExample {

  public static void main(final String[] args) {
     List<String> list = new CopyOnWriteArrayList<>();
    list.add("3");
    list.add("2");
    list.add("1");

    Collections.sort(list);
   }
}

Exception in thread "main" java.lang.UnsupportedOperationException
at java.util.concurrent.CopyOnWriteArrayList$COWIterator.set(CopyOnWriteArrayList.java:1049)
at java.util.Collections.sort(Collections.java:159)
at com.sac.list.CopyOnWriteArrayListExample.main(CopyOnWriteArrayListExample.java:15)  

Thanks in advance.

Answer 1

Collections.sort uses ListIterator.set

    ...
    for (int j=0; j<a.length; j++) {
        i.next();
        i.set((T)a[j]);
    }

but CopyOnWriteArrayList's ListIterator does not support the remove, set or add methods.

Workaround:

    Object[] a = list.toArray();
    Arrays.sort(a);
    for (int i = 0; i < a.length; i++) {
        list.set(i, (String) a[i]);
    }