ArrayDeque.retainAll(Collection) in Java

ArrayDeque.retainAll(Collection<?>): This method is available in java.util.ArrayDeque class of Java.

Syntax:

boolean java.util.ArrayDeque.retainAll(Collection<?> c)

This method takes one argument. This method retains only the elements in this collection that are contained in the specified collection.

Parameters: One parameter is required for this method.

c: a collection containing elements to be retained in this collection.

Returns: true if this collection changed as a result of the call.

Throws:

NullPointerException - if this collection contains one or more null elements and the specified collection does not permit null elements or if the specified collection is null.

Approach 1: When no exception

Java

import java.util.ArrayDeque;

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

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

        arrayDeque.add(1);
        arrayDeque.add(4);
        arrayDeque.add(5);
        arrayDeque.add(3);

        ArrayDeque<Integer> arrayDeque2 = 
                             new ArrayDeque<Integer>();

        arrayDeque2.add(1);
        arrayDeque2.add(2);
        arrayDeque2.add(5);
        arrayDeque2.add(3);

        arrayDeque.retainAll(arrayDeque2);
        System.out.println(arrayDeque.clone());

    }
}

Output:

[1, 5, 3]

Approach 2: NullPointerException

Java

import java.util.ArrayDeque;

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

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

        arrayDeque.add(1);
        arrayDeque.add(4);
        arrayDeque.add(5);
        arrayDeque.add(3);

        ArrayDeque<Integer> arrayDeque2 = null;

        arrayDeque.retainAll(arrayDeque2);
        System.out.println(arrayDeque.clone());

    }
}

Output:

Exception in thread "main" java.lang.NullPointerException
	at java.base/java.util.Objects.requireNonNull(Objects.java:208)
	at java.base/java.util.ArrayDeque.retainAll(ArrayDeque.java:916)