Collection addAll() method in Java with Examples

The addAll(Collection collection) of java.util.Collection interface is used to add the Collection ‘collection’ to this existing collection. This method returns a boolean value depicting the successfulness of the operation. If the collection was added, it returns true, else it returns false.

Syntax:

Collection.addAll(Collection<E> collection)

Parameters: This method accepts a mandatory parameter collection of type Collection which is to be added to this collection.

Return Value: This method returns a boolean value depicting the successfulness of the operation. If the collection was added, it returns true, else it returns false.

Exceptions: This method throws following exceptions:

• UnsupportedOperationException: if the add operation is not supported by this collection
• ClassCastException: if the class of the specified element prevents it from being added to this collection
• NullPointerException: if the specified element is null and this collection does not permit null elements
• IllegalArgumentException: if some property of the element prevents it from being added to this collection
• IllegalStateException: if the element cannot be added at this time due to insertion restrictions

Below examples illustrate the Collection addAll() method:

Example 1: Using LinkedList Class

// Java code to illustrate boolean addAll()

import java.util.*;
import java.util.*;

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

        // Creating an empty LinkedList
        Collection<String>
            list = new LinkedList<String>();

        // A collection is created
        Collection<String>
            collect = new LinkedList<String>();
        collect.add("A");
        collect.add("Computer");
        collect.add("Portal");
        collect.add("for");
        collect.add("Geeks");

        // Displaying the list
        System.out.println("The LinkedList is: " + list);

        // Appending the collection to the list
        list.addAll(collect);

        // displaying the modified LinkedList
        System.out.println("The new linked list is: "
                           + list);
    }
}

Output:

The LinkedList is: []
The new linked list is: [A, Computer, Portal, for, Geeks]

Example 2: Using ArrayDeque Class

// Java code to illustrate addAll() method

import java.util.*;

public class ArrayDequeDemo {
    public static void main(String args[])
    {
        // Creating an empty ArrayDeque
        Collection<String>
            de_que = new ArrayDeque<String>();

        // Creating a new ArrayDeque
        Collection<String>
            deque = new ArrayDeque<String>();
        deque.add("Welcome");
        deque.add("To");
        deque.add("Geeks");
        deque.add("4");
        deque.add("Geeks");

        // Displaying the list
        System.out.println("The ArrayDeque is: " + de_que);

        // Appending the collection to the list
        de_que.addAll(deque);

        // displaying the modified ArrayDeque
        System.out.println("The new ArrayDeque is: "
                           + de_que);
    }
}

Output:

The ArrayDeque is: []
The new ArrayDeque is: [Welcome, To, Geeks, 4, Geeks]

Example 3: Using ArrayList Class

// Java code to illustrate boolean addAll()

import java.util.*;

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

        // Creating an empty ArrayList
        Collection<String>
            list = new ArrayList<String>();

        // A collection is created
        Collection<String>
            collect = new ArrayList<String>();
        collect.add("A");
        collect.add("Computer");
        collect.add("Portal");
        collect.add("for");
        collect.add("Geeks");

        // Displaying the list
        System.out.println("The ArrayList is: " + list);

        // Appending the collection to the list
        list.addAll(collect);

        // displaying the modified ArrayList
        System.out.println("The new ArrayList is: "
                           + list);
    }
}

Output:

The ArrayList is: []
The new ArrayList is: [A, Computer, Portal, for, Geeks]

Example 4: To demonstrate NullPointer Exception

// Java code to illustrate boolean addAll()

import java.util.*;

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

        // Creating an empty ArrayList
        Collection<String>
            list = new ArrayList<String>();

        // A collection is created
        Collection<String> collect = null;

        // Displaying the list
        System.out.println("The ArrayList is: " + list);

        try {
            // Appending the collection to the list
            list.addAll(collect);
        }
        catch (Exception e) {
            System.out.println("Exception: " + e);
        }
    }
}

Output:

The ArrayList is: []
Exception: java.lang.NullPointerException

Reference: https://docs.oracle.com/javase/9/docs/api/java/util/Collection.html#addAll-java.util.Collection-