How to sort an ArrayList? Collection class defines the following two sort methods 1)public static void sort(list l) to sort acc. to default natural sorting order in this list should contains homogeneous object and comparable object otherwise we will get classCastexception list should not contain null otherwise we will get nullPointerException 2)public static void sort(List l,Comparator c) to sort based on customized sorting Do Check My Video On Utility Classes: Example: import java.util.ArrayList; import java.util.Collection; import java.util.Collections; public class Test{ public static void main(String[] args) { ArrayList<String> l = new ArrayList<>(); l.add("z"); l.add("a"); l.add("k"); l.add("n"); // l.add(new Integer(10));//CCE //l.add(null);//NPE System.out.println("Before Sorting: "+l);//[z, a, k, n] Collection