ArrayDeque.addFirst(E) in Java

ArrayDeque.addFirst(E): This method is available in java.util.ArrayDeque class of Java.

Syntax:

void java.util.ArrayDeque.addFirst(E e)

This method takes one argument. This method inserts the specified element at the front of this deque.

Parameters: One parameter is required for this method.

e: the element to add.

Returns: NA

Throws:

NullPointerException - if the specified element is null

Approach 1: When no exception

Java

import java.util.ArrayDeque;

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

        ArrayDeque<Integer> arrayDeque = 
                              new ArrayDeque<Integer>();

        arrayDeque.add(1);
        arrayDeque.addFirst(100);

        System.out.println(arrayDeque.clone());

    }
}

Output:

[100, 1]

Approach 2: NullPointerException

Java

import java.util.ArrayDeque;

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

        ArrayDeque<Integer> arrayDeque = new 
                             ArrayDeque<Integer>();

        arrayDeque.add(1);
        arrayDeque.addFirst(null);

        System.out.println(arrayDeque.clone());

    }
}

Output:

Exception in thread "main" java.lang.NullPointerException
	at java.base/java.util.ArrayDeque.addFirst(ArrayDeque.java:286)