The nullsLast (java.util.Comparator) method returns comparator that is a null-friendly comparator and considers null values greater than non-null. The null first operates by the following logic:
- The null element is considered to be greater than non-null.
- When both elements are null, then they are considered equal.
- When both elements are non-null, the specified Comparator determines the order.
- If specified comparator is null, then the returned comparator considers all non-null elements equal.
- The returned comparator is serializable if the specified comparator is serializable.
Syntax:
static <T> Comparator<T> nullsLast (Comparator<T> comparator)
Parameters: This method accepts a single parameter comparator which is a Comparator for comparing non-null values
Return value: This method returns a comparator that considers null to be greater than non-null and compares non-null objects with the supplied Comparator.
Below programs illustrate nullsLast(java.util.Comparator) method:
Program 1:
// Java program to demonstrate// Comparator.nullsLast (java.util.Comparator) method import java.util.Arrays;import java.util.Comparator; public class GFG { public static void main(String[] args) { // create a collection of an array of names // also contains nulls String[] strings = { "aman", "suvam", null, "sahil", null }; // print the array System.out.println("Before sorting: " + Arrays.toString(strings)); // apply nullsLast method // and sort the array Arrays.sort(strings, Comparator.nullsLast( Comparator.naturalOrder())); // print the array System.out.println("After sorting: " + Arrays.toString(strings)); }} |
The output printed on console of IDE is shown below.
Output:
Program 2:
// Java program to demonstrate// Comparator.nullsLast (java.util.Comparator) method import java.util.Arrays;import java.util.Collections;import java.util.Comparator;import java.util.List;public class GFG { public static void main(String[] args) { // create some user objects User u1 = new User("Aaman", 25); User u2 = new User("Joyita", 22); User u3 = new User("Suvam", 28); User u4 = new User("mahafuj", 25); System.out.println("One null Objects"); List<User> list = Arrays.asList(u1, u2, u3, null, u4); Collections.sort(list, Comparator.nullsLast( Comparator.comparing( User::getName))); list.forEach(user -> System.out.println(user)); System.out.println("\nMore than One null Objects"); list = Arrays.asList(u1, u4, null, u2, u3, null, null); Collections.sort(list, Comparator.nullsLast( Comparator.comparing( User::getName))); list.forEach(user -> System.out.println(user)); }}class User implements Comparable<User> { public String name; public int age; public User(String name, int age) { this.name = name; this.age = age; } public int compareTo(User u1) { return name.compareTo(u1.name); } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } @Override public String toString() { return "User [name=" + name + ", age=" + age + "]"; }} |
The output printed on console is shown below.
Output:
References: https://docs.oracle.com/javase/10/docs/api/java/util/Comparator.html#nullsLast(java.util.Comparator)
