ConcurrentSkipListSet ceiling() method in Java

The java.util.concurrent.ConcurrentSkipListSet.ceiling() method is an in-built function in Java which returns the least element in this set greater than or equal to the given element, or null if there is no such element.

Syntax:

 ConcurrentSkipListSet.ceiling(E e)

Parameters: The function accepts a single parameter e i.e. the element to match.

Return Value: The function returns the least element greater than or equal to e, or null if there is no such element.

Exception: The function shows the following exceptions:

ClassCastException – if the specified element cannot be compared with the elements currently in the set

NullPointerException – if the specified element is null

Below programs illustrate the ConcurrentSkipListSet.ceiling() method:

Program 1: To find ceiling of a number.

// Java Program Demonstrate ceiling()
// method of ConcurrentSkipListSet

import java.util.concurrent.*;

class ConcurrentSkipListSetCeilingExample1 {
    public static void main(String[] args)
    {
        // Creating a set object
        ConcurrentSkipListSet<Integer> Lset =
                        new ConcurrentSkipListSet<Integer>();

        // Adding elements to this set
        Lset.add(45);
        Lset.add(72);
        Lset.add(31);
        Lset.add(13);
        Lset.add(89);

        // Printing elements of the set
        System.out.println("The set contains: ");
        for (Integer i : Lset)
            System.out.print(i + " ");

        // Ceiling of 35
        System.out.println("\nCeiling of 35: " + Lset.ceiling(35));

        // Ceiling of 100
        System.out.println("\nCeiling of 100: " + Lset.ceiling(100));
    }
}

Output:

The set contains: 
13 31 45 72 89 
Ceiling of 35: 45

Ceiling of 100: null

Program 2: To show NullPointerException in ceiling().

// Java Program Demonstrate ceiling()
// method of ConcurrentSkipListSet

import java.util.concurrent.*;
import java.io.*;

class ConcurrentSkipListSetCeilingExample2 {
    public static void main(String[] args) throws IOException
    {
        // Creating a set object
        ConcurrentSkipListSet<Integer> Lset =
                            new ConcurrentSkipListSet<Integer>();

        // Adding elements to this set
        Lset.add(45);
        Lset.add(72);
        Lset.add(31);
        Lset.add(13);
        Lset.add(89);

        try {
            // Ceiling of null
            System.out.println("Ceiling of null: " + Lset.ceiling(null));
        }

        catch (Exception e) {
            System.out.println("Exception : " + e);
        }
    }
}

Output:

Exception : java.lang.NullPointerException

Reference : https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ConcurrentSkipListSet.html#ceiling(E)