List listWithoutDup = new ArrayList(new HashSet(listWithDup));

List<string> listWithoutDup = new ArrayList<string>(new HashSet<string>(listWithDup));

List<string> listWithoutDup = new ArrayList<>(new HashSet<>(listWithDup));

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
 
public class Test {
 public static void main(String[] args) {
 List<string> listWithDup = new ArrayList<string>();
 listWithDup.add("1");
 listWithDup.add("2");
 listWithDup.add("3");
 listWithDup.add("1");
 
 List<string> listWithoutDup = new ArrayList<string>(new HashSet<string>(listWithDup));
 System.out.println("list with dup:"+ listWithDup);
 System.out.println("list without dup:"+ listWithoutDup);
 }
}