ConcurrentLinkedDeque peekFirst() method in Java

Last Updated : 26 Nov, 2018

The java.util.concurrent.ConcurrentLinkedDeque.peekFirst() is an in-built method in Java which retrieves the first element of this deque without removing it. The function returns NULL if the deque is empty. Syntax:

Conn_Linked_Deque.peekFirst()

Parameters: This function does not accepts any parameter. Return Values: The function returns the first element present in this deque and returns NULL when the deque is empty. Below programs illustrate the peekFirst() method: Program 1: This program involves deque with Integer elements.

Java

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

import java.util.concurrent.*;

class ConcurrentLinkedDequeDemo {
    public static void main(String[] args)
    {
        ConcurrentLinkedDeque<Integer> cld =
                    new ConcurrentLinkedDeque<Integer>();

        cld.addFirst(12);
        cld.addFirst(110);
        cld.addFirst(55);
        cld.addFirst(76);

        // Displaying the existing LinkedDeque
        System.out.println("Elements in"
                           + "the LinkedDeque: " + cld);

        // Displaying the first element
        System.out.println("First Element in"
                   + "the LinkedDeque: " + cld.peekFirst());
    }
}

Output:

Elements inthe LinkedDeque: [76, 55, 110, 12]
First Element inthe LinkedDeque: 76

Program 2: This program involves deque with String elements.

Java

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

import java.util.concurrent.*;

class ConcurrentLinkedDequeDemo {
    public static void main(String[] args)
    {
        ConcurrentLinkedDeque<String> cld = 
                           new ConcurrentLinkedDeque<String>();

        cld.addFirst("GFG");
        cld.addFirst("Gfg");
        cld.addFirst("GeeksforGeeks");
        cld.addFirst("Geeks");

        // Displaying the existing LinkedDeque
        System.out.println("Elements in"
                           + "the LinkedDeque: " + cld);

        // Displaying the First element
        System.out.println("First Element in"
                       + "the LinkedDeque: " + cld.peekFirst());
    }
}

Output:

Elements inthe LinkedDeque: [Geeks, GeeksforGeeks, Gfg, GFG]
First Element inthe LinkedDeque: Geeks

Reference:https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentLinkedDeque.html#peekFirst()

ConcurrentLinkedDeque removeFirst() method in Java

RICHIK BHATTACHARJEE

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