import java.util.*;

class Example {
    public static void main(String[] args) {
        List<?> list = new ArrayList<>(Arrays.asList("test"));
        modify(list);
    }
    
    static <T> void modify(List<T> list) {
        list.add(list.get(0));
        list.add(list.get(0));
        
        System.out.println(list);
    }
}