ArrayList.addAll() in Java

ArrayList.addAll(): This method is available in java.util.ArrayList class of Java.

Syntax:

boolean java.util.ArrayList.addAll(Collection<? extends E> c)

This method takes one argument. This method appends all of the elements in the specified collection to the end of this list, in the order that they are returned by the specified collection's Iterator.

Parameters: One parameter is required for this method.

c: a collection containing elements to be added to this list.

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

Throws:

1. NullPointerException - if the specified collection is null

Approach 1: When no exceptions

Java

import java.util.ArrayList;

public class ArrayListAddAll {
    public static void main(String[] args) {
        ArrayList<Integer> arr = new ArrayList<>();
        ArrayList<Integer> arr1 = new ArrayList<Integer>();
        arr1.add(1);
        arr1.add(2);
        // Add all in arr
        arr.addAll(arr1);

        System.out.println("arr: ");
        arr.forEach((n -> System.out.print(n + " ")));

        System.out.println();
        System.out.println("arr1: ");
        arr1.forEach((n -> System.out.print(n + " ")));
    }
}

Output:

arr: 

1 2 

arr1: 

1 2 

Approach 2: NullPointerException 

Java

import java.util.ArrayList;

public class ArrayListAddAll {
    public static void main(String[] args) {
        ArrayList<Integer> arr = new ArrayList<>();
        ArrayList<Integer> arr1 = null;

        // Add all in arr
        arr.addAll(arr1);

        System.out.println("arr: ");
        arr.forEach((n -> System.out.print(n + " ")));

        System.out.println();
        System.out.println("arr1: ");
        arr1.forEach((n -> System.out.print(n + " ")));
    }
}

Output:

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "java.util.Collection.toArray()" because "c" is null
	at java.base/java.util.ArrayList.addAll(ArrayList.java:670)