ConcurrentSkipListSet floor() method in Java

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

Syntax:

ConcurrentSkipListSet.floor(E e)

Parameter: The function accepts a single parameter e i.e. the value to match.

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

Exception: The function throws 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.floor() method:

Program 1:

// Java program to demonstrate floor()
// method of ConcurrentSkipListSet

import java.util.concurrent.*;

class ConcurrentSkipListSetFloorExample1 {
    public static void main(String[] args)
    {
        // Creating a set object
        ConcurrentSkipListSet<Integer>
            Lset = new ConcurrentSkipListSet<Integer>();

        // Adding elements to this set
        for (int i = 10; i <= 50; i += 10)
            Lset.add(i);

        // Finding floor of 20 in the set
        System.out.println("The floor of 20 in the set "
                           + Lset.floor(20));

        // Finding floor of 39 in the set
        System.out.println("The floor of 39 in the set "
                           + Lset.floor(39));

        // Finding floor of 9 in the set
        System.out.println("The floor of 10 in the set "
                           + Lset.floor(9));
    }
}

Output:

The floor of 20 in the set 20
The floor of 39 in the set 30
The floor of 10 in the set null

Program 2: Program to show NullPointerException in floor().

// Java program to demonstrate floor()
// method of ConcurrentSkipListSet

import java.util.concurrent.*;

class ConcurrentSkipListSetFloorExample2 {
    public static void main(String[] args)
    {
        // Creating a set object
        ConcurrentSkipListSet<Integer>
            Lset = new ConcurrentSkipListSet<Integer>();

        // Adding elements to this set
        for (int i = 10; i <= 50; i += 10)
            Lset.add(i);

        // Trying to find the floor of null
        try {
            System.out.println("The floor of null in the set "
                               + Lset.floor(null));
        }
        catch (Exception e) {
            System.out.println("Exception: " + e);
        }
    }
}

Output:

Exception: java.lang.NullPointerException

Reference: https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentSkipListSet.html#floor-E-