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 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 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("Lazyroar");        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, Lazyroar, Gfg, GFG] First Element inthe LinkedDeque: Geeks
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