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)
