The java.util.ArrayDeque.poll() method in Java is used to retrieve or fetch and remove the element present at the head of the Deque. The peek() method only retrieved the element at the head but the poll() also removes the element along with the retrieval. It returns NULL if the deque is empty.
Syntax:
Array_Deque.poll()
Parameters: The method does not take any parameter.
Return Value: The method removes the element at the head of the Deque and returns the same. It returns NULL if the deque is empty.
Below programs illustrate the Java.util.ArrayDeque.poll() method:
Program 1:
// Java code to illustrate poll()import java.util.*;  public class ArrayDequeDemo {    public static void main(String args[])    {        // Creating an empty ArrayDeque        Deque<String> de_que = new ArrayDeque<String>();          // Use add() method to add elements into the Deque        de_que.add("Welcome");        de_que.add("To");        de_que.add("Geeks");        de_que.add("4");        de_que.add("Geeks");          // Displaying the ArrayDeque        System.out.println("ArrayDeque: " + de_que);          // Displaying the head        System.out.println("The element at head is: "                                            + de_que.poll());          // Displaying the final ArrayDeque        System.out.println("ArrayDeque after operation: "                                                    + de_que);    }} |
Output:
ArrayDeque: [Welcome, To, Geeks, 4, Geeks] The element at head is: Welcome ArrayDeque after operation: [To, Geeks, 4, Geeks]
Program 2:
// Java code to illustrate poll()import java.util.*;  public class ArrayDequeDemo {    public static void main(String args[])    {        // Creating an empty ArrayDeque        Deque<Integer> de_que = new ArrayDeque<Integer>();          // Use add() method to add elements into the Deque        de_que.add(10);        de_que.add(15);        de_que.add(30);        de_que.add(20);        de_que.add(5);          // Displaying the ArrayDeque        System.out.println("ArrayDeque: " + de_que);          // Displaying the head        System.out.println("The element at head is: "                                          + de_que.poll());          // Displaying the final ArrayDeque        System.out.println("ArrayDeque after operation: "                                                 + de_que);    }} |
Output:
ArrayDeque: [10, 15, 30, 20, 5] The element at head is: 10 ArrayDeque after operation: [15, 30, 20, 5]
Program 3: For an empty deque:
// Java code to illustrate poll()import java.util.*;  public class ArrayDequeDemo {    public static void main(String args[])    {        // Creating an empty ArrayDeque        Deque<Integer> de_que = new ArrayDeque<Integer>();          // Displaying the ArrayDeque        System.out.println("ArrayDeque: " + de_que);          // Displaying the head        System.out.println("The element at head is: " +                                            de_que.poll());    }} |
Output:
ArrayDeque: [] The element at head is: null
