Open In App

Comparator nullsLast() method in Java with examples

Improve
Improve
Improve
Like Article
Like
Save Article
Save
Share
Report issue
Report

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:

  1. The null element is considered to be greater than non-null.
  2. When both elements are null, then they are considered equal.
  3. When both elements are non-null, the specified Comparator determines the order.
  4. If specified comparator is null, then the returned comparator considers all non-null elements equal.
  5. 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)



Last Updated : 29 Apr, 2019
Like Article
Save Article
Previous
Next
Share your thoughts in the comments
Similar Reads