We can USE a HashSet to do the job of removing the DUPLICATE elements. HashSet only stores UNIQUE elements and we'll use that FEATURE of HashSet to remove duplicates.

If you have a LIST called cityList you can create a HashSet using this list - 

Set<String> citySet = new HashSet<String>(cityList);
then add this set back to the cityList 
cityList.clear();
cityList.addAll(citySet);

That will remove all the duplicate elements from the given list. Note that insertion order won't be retained if a HashSet is used. In case insertion order is to be retained use LinkedHashSet.

We can use a HashSet to do the job of removing the duplicate elements. HashSet only stores unique elements and we'll use that feature of HashSet to remove duplicates.

If you have a List called cityList you can create a HashSet using this list - 

Set<String> citySet = new HashSet<String>(cityList);
then add this set back to the cityList 
cityList.clear();
cityList.addAll(citySet);

That will remove all the duplicate elements from the given list. Note that insertion order won't be retained if a HashSet is used. In case insertion order is to be retained use LinkedHashSet.