Exception in thread "main" java.util.ConcurrentModificationException
        at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:372)
        at java.util.AbstractList$Itr.next(AbstractList.java:343)
        at ContactTree.nonuniName(ContactTree.java:270)
        at ContactTree.nonuniName(ContactTree.java:296)
        at ContactTree.nonuniName(ContactTree.java:296)
        at ContactTree.nonuniName(ContactTree.java:295)
        at ContactTree.nonuniName(ContactTree.java:296)
        at ContactTree.nonuniName(ContactTree.java:296)
        at ContactTree.nonuniName(ContactTree.java:295)
        at ContactTree.nonuniName(ContactTree.java:296)
        at ContactTree.nonuniName(ContactTree.java:296)
        at ContactTree.nonuniName(ContactTree.java:296)
        at ContactTree.nonuniName(ContactTree.java:296)
        at ContactTree.nonuniName(ContactTree.java:295)
        at ContactTree.nonuniName(ContactTree.java:296)
        at ContactTree.nonuniName(ContactTree.java:295)
        at ContactTree.nonuniName(ContactTree.java:295)
        at ContactTree.nonuniName(ContactTree.java:247)
        at Oblig1.main(Oblig1.java:49)