The java.util.concurrent.ConcurrentLinkedDeque.offerFirst() method is an inbuilt method in Java which inserts the specified element, passed as a parameter, in the front of the deque.
Syntax:
Conn_Linked_Deque.offerFirst(Object elem)
Parameters: The method accepts a parameter elem which species the element to be inserted to the front of the deque.
Return Value: The function returns True if the element is successfully added into the deque and returns False otherwise.
Exception: The function throws a NullPointerException if the passed parameter is NULL.
Below programs illustrate the ConcurrentLinkedDeque.offerFirst() method:
Program 1:
/* Java Program to Demonstrate offerFirst()   method of ConcurrentLinkedDeque */  import java.util.concurrent.*;class GFG {    public static void main(String[] args)    {          // Creating an empty Deque        ConcurrentLinkedDeque<String> cld =                      new ConcurrentLinkedDeque<String>();          // Add elements into the Deque        cld.add("Welcome");        cld.add("To");        cld.add("Geeks");        cld.add("4");        cld.add("Geeks");          // Displaying the Deque        System.out.println("Elements in Deque: "                           + cld);          // Displaying the First element        System.out.println("The First element is: " +                                        cld.getFirst());          /* Insert an element at the front            of the deque */        if (cld.offerFirst("GFG")) {            // Displaying the First element            System.out.println("The Inserted element is: " +                                              cld.getFirst());        }          // Displaying the Deque        System.out.println("Elements in Deque: "                           + cld);          // Displaying the First element        System.out.println("The First element is: " +                                       cld.getFirst());    }} |
Output:
Elements in Deque: [Welcome, To, Geeks, 4, Geeks] The First element is: Welcome The Inserted element is: GFG Elements in Deque: [GFG, Welcome, To, Geeks, 4, Geeks] The First element is: GFG
Program 2:
/* Java Program to Demonstrate offerFirst()   method of ConcurrentLinkedDeque */  import java.util.concurrent.*;class GFG {    public static void main(String[] args)    {          // Creating an empty Deque        ConcurrentLinkedDeque<Integer> cld =                   new ConcurrentLinkedDeque<Integer>();          // Add elements into the Deque        cld.add(12);        cld.add(43);        cld.add(29);        cld.add(16);        cld.add(70);          // Displaying the Deque        System.out.println("Elements in Deque: "                           + cld);          // Displaying the First element        System.out.println("The First element is: " +                                      cld.getFirst());          try {            cld.offerFirst(null);        }        catch (Exception e) {            System.out.println(e);        }          /* Insert an element at the front            of the deque */        if (cld.offerFirst(74)) {            // Displaying the First element            System.out.println("The Inserted element is: " +                                             cld.getFirst());        }          // Displaying the Deque        System.out.println("Elements in Deque: "                           + cld);          // Displaying the First element        System.out.println("The First element is: " +                                       cld.getFirst());    }} |
Output:
Elements in Deque: [12, 43, 29, 16, 70] The First element is: 12 java.lang.NullPointerException The Inserted element is: 74 Elements in Deque: [74, 12, 43, 29, 16, 70] The First element is: 74
