removing duplicate values from sql table added in arraylist

First check the query if you can eliminate duplicate values from the query itself. Even if you can't , then use LinkedHashMap.

you have to use LinkedHashSet, which store only unique data i.e no duplicate data allow in LinkedHashSet. also,it store data in same sequence as ArrayList.

or use this code-

List<String> list = new ArrayList<>();

// add elements to list, including duplicates

Set<String> hs = new LinkedHashSet<>();

hs.addAll(list);

list.clear();

list.addAll(hs);

As its a String, you can use Set data structure to hold these values, which doesn't contain the duplicate values.

Read more about set here.

Sample code of HashSet :-

public class SetEx {

public static void main(String args[])
{
    Set<String> set = new HashSet<String>();
    set.add("abc");
    set.add("aaa");
    set.add("fgh");
    set.add("hdsjkadhka");
    set.add("abc");
    set.add("aaa");

    System.out.println("set of Strings " + set);
}

}

Edit :- if you want to create a HashSet from existing ArrayList then use below code :-

 ArrayList<String> list = new ArrayList<>();
        list.add("amit");
        list.add("amit");

        Set<String> copySet = new HashSet<>(list);

        System.out.println("set of string "+ copySet);

Using Java 8 Streams:

List<String> listWithDups = getListWithDupes();
//do something else before remove dupes
List<String> result = listWithDups.stream()
    .distinct()
    .collect(Collector.toList());
//Use your new list

Also, if you obtain duplicated values from your SQL query, you should consider using DISTINCT keyword in your query.