When working with collections in Java, one common dilemma is choosing between LinkedList and ArrayList. Both implement the List interface but have distinct differences in their internal workings and performance implications for various operations. This tutorial aims to shed light on LinkedList vs. ArrayList to help you decide which to use based on your specific needs.
Understanding ArrayList
ArrayList is essentially a resizable array. It provides fast access to its elements since it uses an index-based system for element retrieval.
Key Characteristics:
- Random Access:
ArrayListallows quick retrieval of elements because it operates on an array. Access time is O(1) for any element. - Size Flexibility: The size of an
ArrayListcan grow or shrink dynamically as elements are added or removed. - Performance Considerations: Adding or removing elements from anywhere but the end of the
ArrayListrequires shifting elements, which can be costly. Adding elements is O(n) in the worst case but amortized to O(1).
Use Case Scenario for ArrayList:
- Ideal for situations with frequent read operations and infrequent write operations, especially when additions and deletions are primarily at the end of the list.
Understanding LinkedList
LinkedList, as the name suggests, is implemented as a doubly-linked list. Each element (node) in the list contains references to both the next and the previous node.
Key Characteristics:
- Sequential Access: Access time for an element is linear, O(n), as it may need to traverse the list from the beginning or end to reach the desired element.
- Element Insertion and Deletion: Adding or removing elements from a
LinkedListis generally faster compared to anArrayList, especially for operations at the head or middle of the list, as it doesn’t require element shifting—just changing the node links. - Memory Overhead: Each element in a
LinkedListholds two references (next and previous), which adds memory overhead.
Use Case Scenario for LinkedList:
- Suited for applications that require frequent insertions and deletions of elements from any part of the list or implementing stack/queue data structures.
LinkedList vs. ArrayList: Comparison
| Feature | ArrayList |
LinkedList |
|---|---|---|
| Internal Structure | Resizable Array | Doubly-Linked List |
| Access Time | Fast (O(1)) | Slow (O(n)) |
| Insertion/Deletion at Ends | Fast (Amortized O(1)) | Very Fast (O(1)) |
| Insertion/Deletion in Middle | Slow (O(n)) | Faster (O(1) for the operation, but finding the position is O(n)) |
| Memory Efficiency | More efficient (only stores elements) | Less efficient (stores elements + two references per element) |
| Iteration | Fast | Slower than ArrayList |
| Use Case | Frequent reads, infrequent writes | Frequent writes, infrequent reads |
Decision Making: Which Should You Use?
ArrayList: Choose when you need fast access to elements using index. It’s generally preferred for storing and accessing data where the primary operations are retrieval of elements.LinkedList: Opt forLinkedListwhen your application involves frequent addition and removal of elements from any part of the list. It’s also ideal for implementing queues and stacks where elements are continuously added and removed.
Let’s enhance our exploration of LinkedList vs. ArrayList in Java with code examples, illustrating how their characteristics translate into practical application differences.
Example 1: Adding Elements
ArrayList – Adding elements at the end
|
1 2 3 4 5 6 |
import java.util.ArrayList; ArrayList<Integer> arrayList = new ArrayList<>(); arrayList.add(1); // Fast arrayList.add(2); // Fast System.out.println("ArrayList: " + arrayList); |
LinkedList – Adding elements at the beginning
|
1 2 3 4 5 6 |
import java.util.LinkedList; LinkedList<Integer> linkedList = new LinkedList<>(); linkedList.addFirst(1); // Very fast linkedList.addFirst(2); // Very fast System.out.println("LinkedList: " + linkedList); |
Output:
|
1 2 |
ArrayList: [1, 2] LinkedList: [2, 1] |
Explanation: Adding elements at the end of an ArrayList is efficient due to its array-based structure. For a LinkedList, adding elements at the beginning or end is very efficient due to its linked nature, without the need for element shifting.
Example 2: Random Access
Accessing Elements by Index
|
1 2 3 4 5 6 7 |
// Continuing from the previous ArrayList Integer num = arrayList.get(1); // Fast access System.out.println("Accessed from ArrayList: " + num); // LinkedList num = linkedList.get(1); // Slower access compared to ArrayList System.out.println("Accessed from LinkedList: " + num); |
Output:
|
1 2 |
Accessed from ArrayList: 2 Accessed from LinkedList: 1 |
Explanation: ArrayList provides faster random access to its elements due to direct indexing. In contrast, LinkedList must traverse the links to reach the specified index, which takes longer.
Example 3: Insertion in the Middle
Inserting Elements in the Middle
|
1 2 3 4 5 6 7 |
// ArrayList arrayList.add(1, 100); // Slower as it may require shifting System.out.println("ArrayList after insertion: " + arrayList); // LinkedList linkedList.add(1, 100); // Faster insertion than ArrayList System.out.println("LinkedList after insertion: " + linkedList); |
Output:
|
1 2 |
ArrayList after insertion: [1, 100, 2] LinkedList after insertion: [2, 100, 1] |
Explanation: Insertions in the middle of an ArrayList are slower because elements need to be shifted to make space. LinkedList can insert more efficiently by just changing the links of the adjacent nodes.
Example 4: Memory Overhead
There’s no direct way to demonstrate memory overhead in simple code examples without delving into profiling and analysis. However, it’s important to remember that each LinkedList element requires additional memory for storing the references to the next and previous elements, while ArrayList elements do not.
Conclusion
These examples illustrate the practical differences between ArrayList and LinkedList. ArrayList excels in scenarios requiring frequent, random access to elements, whereas LinkedList is more efficient for scenarios involving frequent additions and removals, especially at the ends or in the middle of the list. The choice between them should be guided by the specific requirements of your application, considering the trade-offs in performance, memory usage, and the types of operations you’ll be performing most frequently.