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NavigableSet pollFirst() method in Java
  • Difficulty Level : Medium
  • Last Updated : 29 Sep, 2018

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)

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