Java LinkedList addAll() Method

The LinkedList.addAll() method in Java is used to add all elements from a specified collection to a LinkedList. This guide will cover the method’s usage, explain how it works, and provide examples to demonstrate its functionality, including its overloaded methods.

Table of Contents

1. Introduction
2. addAll Method Syntax
3. Examples
   • Adding All Elements from a Collection
   • Adding All Elements from a Collection at a Specific Index
   • Handling Null Collections
4. Conclusion

Introduction

The LinkedList.addAll() method is a member of the LinkedList class in Java. It allows you to add all elements from a specified collection to a LinkedList, either at the end of the list or at a specific position. This method is particularly useful for combining collections or extending a LinkedList with multiple elements at once.

addAll Method Syntax

The syntax for the addAll method is as follows:

Adding All Elements to the End

public boolean addAll(Collection<? extends E> c)

• c: The collection containing elements to be added to the end of the LinkedList.

Adding All Elements at a Specific Index

public boolean addAll(int index, Collection<? extends E> c)

• index: The index at which the specified collection is to be inserted.
• c: The collection containing elements to be added.

Examples

Adding All Elements from a Collection

The addAll method can be used to add all elements from a collection to the end of a LinkedList.

Example

import java.util.LinkedList;
import java.util.ArrayList;

public class AddAllExample {
    public static void main(String[] args) {
        // Creating a LinkedList of Strings
        LinkedList<String> list = new LinkedList<>();

        // Adding elements to the LinkedList
        list.add("Apple");
        list.add("Banana");

        // Creating another collection (ArrayList) of Strings
        ArrayList<String> moreFruits = new ArrayList<>();
        moreFruits.add("Orange");
        moreFruits.add("Grapes");

        // Adding all elements from the ArrayList to the LinkedList
        list.addAll(moreFruits);

        // Printing the LinkedList
        System.out.println("LinkedList: " + list);
    }
}

Output:

LinkedList: [Apple, Banana, Orange, Grapes]

Adding All Elements from a Collection at a Specific Index

You can add all elements from a collection at a specific position in the LinkedList using the addAll method with an index.

Example

import java.util.LinkedList;
import java.util.ArrayList;

public class AddAllExample {
    public static void main(String[] args) {
        // Creating a LinkedList of Strings
        LinkedList<String> list = new LinkedList<>();

        // Adding elements to the LinkedList
        list.add("Apple");
        list.add("Banana");

        // Creating another collection (ArrayList) of Strings
        ArrayList<String> moreFruits = new ArrayList<>();
        moreFruits.add("Orange");
        moreFruits.add("Grapes");

        // Adding all elements from the ArrayList to the LinkedList at index 1
        list.addAll(1, moreFruits);

        // Printing the LinkedList
        System.out.println("LinkedList: " + list);
    }
}

Output:

LinkedList: [Apple, Orange, Grapes, Banana]

Handling Null Collections

The addAll method will throw a NullPointerException if the specified collection is null.

Example

import java.util.LinkedList;

public class AddAllExample {
    public static void main(String[] args) {
        // Creating a LinkedList of Strings
        LinkedList<String> list = new LinkedList<>();

        // Adding elements to the LinkedList
        list.add("Apple");
        list.add("Banana");

        try {
            // Attempting to add elements from a null collection
            list.addAll(null);
        } catch (NullPointerException e) {
            System.out.println("Exception: " + e);
        }

        // Printing the LinkedList
        System.out.println("LinkedList: " + list);
    }
}

Output:

Exception: java.lang.NullPointerException
LinkedList: [Apple, Banana]

Conclusion

The LinkedList.addAll() method in Java provides a convenient way to add all elements from a specified collection to a LinkedList. By understanding how to use this method and its overloaded versions, you can efficiently manage and combine collections of objects in your Java applications. Whether you are adding all elements to the end of the list or inserting them at specific positions, the addAll method offers a flexible solution for these tasks.