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Last Updated on November 23, 2023 by Ankit Kochar

In the world of Java programming, the LinkedList data structure holds a significant place due to its dynamic nature and flexible operations. One of the key methods enhancing its functionality is addAll(). This method provides a convenient way to merge or append elements from one LinkedList into another, streamlining the process of combining lists. Understanding its nuances and optimal usage can significantly improve code efficiency and readability in Java development.

## Approach and Algorithm (addAll(Collection X))

LinkedList.addAll(Collection X) : In this method, we pass a Collection X as a parameter to this function. As a result, this function appends all the elements of the collection passed to the end of the list and also while appending it keeps in mind the order of return by the collection’s iterator.

Syntax : boolean addAll(Collection X)

It returns true only if at least a single action of append is performed.

### Code Implementation

```import java.util.*;
import java.util.ArrayList;

public static void main(String args[]) {

Collection<String> collect = new ArrayList<String>();

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

System.out.println("The new linked list is: " + list);

}
}
```

#### Output

The LinkedList is: [Coding, is, Fun, 10, 20]
The new linked list is: [Coding, is, Fun, 10, 20, A, Computer, Game]

Time Complexity: O(n), where n is the size of the collection to be added.
Space Complexity: O(n), where n is the size of the collection to be added.

### Approach and Algorithm (addAll(int index,Collection X))

LinkedList.addAll(int index,Collection X) : In this method, we pass a Collection X and an index as parameters to this function. As a result, this function appends all the elements of the collection to the list at a specified index of the list that is passed as a parameter.

Syntax : boolean addAll(int index, Collection X)

It returns true only if at least a single action of append is performed.

### Code Implementation

```import java.util.*;
import java.util.ArrayList;

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

Collection<string> collect = new ArrayList<string>();

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

System.out.println("The new linked list is: " + list);

}
}
```

#### Output

The LinkedList is: [Coding, is, 10, 20]
The new linked list is: [Coding, PrepBytes, Placement, Program, for, Students, is, 10, 20]

Time Complexity: O(n), where n is the size of the collection to be added.
[forminator_quiz id=”4042″]

Conclusion
In conclusion, the addAll() method in Java LinkedLists is a powerful tool for merging or appending collections, offering flexibility and convenience in managing lists. Whether consolidating multiple lists or simply appending elements, this method streamlines the process with its straightforward implementation. Mastery of addAll() enhances code readability, improves efficiency, and empowers Java developers to handle complex data structures with ease.

## FAQ (Frequently Asked Questions) Related to Linkedlist addAll() Method in Java:

Here are some FAQs related to Linkedlist addAll() Method in Java.

1. How does addAll() differ from add() in Java LinkedLists?
add() is used to append a single element at the end of the LinkedList, whereas addAll() is employed to append or merge an entire collection of elements (another LinkedList, an array, etc.) to the end of the existing LinkedList.

2. Can addAll() be used to merge LinkedLists of different types in Java?
No, addAll() expects the collections being merged to be of the same type. Attempting to merge LinkedLists of different types might result in a ClassCastException.

3. What happens if the collection passed to addAll() contains null elements?
addAll() allows the addition of null elements. If the collection passed has null elements, they will be added to the target LinkedList along with the other elements.

4. Does addAll() modify the original LinkedList?
Yes, addAll() does modify the target LinkedList by appending or merging the elements from the specified collection without creating a new LinkedList.

5. Are there any performance considerations when using addAll()?
The performance of addAll() can vary depending on the size of the LinkedLists being merged. For large LinkedLists, the time complexity might be higher due to the need to iterate through all elements.