NavigableSet pollFirst() method in Java

The pollFirst() method of NavigableSet interface in Java is used to retrieves and removes the first (lowest) element, or returns null if this set is empty.

Syntax:

E pollFirst()

Where, E is the type of elements maintained by this Set container.

Parameters: This function does not accepts any parameter.

Return Value: It returns returns null if this set is empty.

Below programs illustrate the pollFirst() method in Java:

Program 1: NavigableSet with integer elements.

// A Java program to demonstrate
// pollFirst() method of NavigableSet

import java.util.NavigableSet;
import java.util.TreeSet;

public class GFG {
    public static void main(String[] args)
    {
        NavigableSet<Integer> ns = new TreeSet<>();
        ns.add(0);
        ns.add(1);
        ns.add(2);
        ns.add(3);
        ns.add(4);
        ns.add(5);
        ns.add(6);

        System.out.println("First lowest element removed is : "
                                              + ns.pollFirst());
    }
}

Output:

First lowest element removed is : 0

Program 2: NavigableSet with string elements.

// A Java program to demonstrate
// pollFirst() method of NavigableSet

import java.util.NavigableSet;
import java.util.TreeSet;

public class GFG {
    public static void main(String[] args)
    {
        NavigableSet<String> ns = new TreeSet<>();
        ns.add("A");
        ns.add("B");
        ns.add("C");
        ns.add("D");
        ns.add("E");
        ns.add("F");
        ns.add("G");

        System.out.println("First lowest element removed is : "
                                              + ns.pollFirst());
    }
}

Output:

First lowest element removed is : A

Reference: https://docs.oracle.com/javase/10/docs/api/java/util/NavigableSet.html#pollFirst(E)