Question

Is there a Java data structure that:

• does not allow duplicates
• retains insertion order
• allows removal and insertion at either the start or end of the collection

There is LinkedHashSet, but it only allows remove(object), add(object) as per Set.

Answer 1

LinkedHashSet will allow removal of the first element, just do

Iterator iter = linkedHashSet.iterator();
if(iter.next()) {
   iter.remove();
}