LinkedBlockingDeque peekFirst() method in Java

The peekFirst() method of LinkedBlockingDeque returns the front element in the Deque container, but does not deletes it. It returns null if the container is empty.

Syntax:

public E peekFirst()

Parameters: This method does not accept any parameters.

Returns: This method returns front element in the Deque container if the container is not empty. It returns null if the container is empty.

Below programs illustrate peekFirst() method of LinkedBlockingDeque:

Program 1:

// Java Program Demonstrate peekFirst()
// method of LinkedBlockingDeque

import java.util.concurrent.LinkedBlockingDeque;
import java.util.*;

public class GFG {
    public static void main(String[] args)

    {

        // create object of LinkedBlockingDeque
        LinkedBlockingDeque<Integer> LBD
            = new LinkedBlockingDeque<Integer>();

        // Add numbers to end of LinkedBlockingDeque
        LBD.addFirst(7855642);
        LBD.addFirst(35658786);
        LBD.addFirst(5278367);
        LBD.addFirst(74381793);

        // Print the queue
        System.out.println("Linked Blocking Deque: " + LBD);

        System.out.println("Front element in Deque: " +
                                        LBD.peekFirst());
    }
}

Output:

Linked Blocking Deque: [74381793, 5278367, 35658786, 7855642]
Front element in Deque: 74381793

Program 2:

// Java Program Demonstrate peekFirst()
// method of LinkedBlockingDeque
// when Deque is empty

import java.util.concurrent.LinkedBlockingDeque;
import java.util.*;

public class GFG {
    public static void main(String[] args)

    {

        // create object of LinkedBlockingDeque
        LinkedBlockingDeque<Integer> LBD
            = new LinkedBlockingDeque<Integer>();

        // Add numbers to end of LinkedBlockingDeque
        LBD.add(7855642);
        LBD.add(35658786);
        LBD.add(5278367);
        LBD.add(74381793);

        // Print the queue
        System.out.println("Linked Blocking Deque: " + LBD);

        // empty deque
        LBD.clear();

        System.out.println("Front element in Deque: " +
                                          LBD.peekFirst());
    }
}

Output:

Linked Blocking Deque: [7855642, 35658786, 5278367, 74381793]
Front element in Deque: null

Reference: https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/LinkedBlockingDeque.html#peekFirst()