ArrayList vs LinkedList: Complete Guide

ArrayList is almost always the preferred choice for most Java applications due to its superior performance in common scenarios, but LinkedList excels in specific situations involving frequent insertions and deletions at both ends of the list, and when random access isn’t required. The decision ultimately depends on your specific use case patterns, with ArrayList being optimal for index-based operations and modifications at the end, while LinkedList shines for queue-like operations and frequent structural changes.

Contents

• Internal Architecture Differences
• Performance Characteristics
• When to Use LinkedList Over ArrayList
• When to Stick with ArrayList
• Specific Use Case Examples
• Performance Benchmarks
• Best Practices

Internal Architecture Differences

ArrayList and LinkedList are fundamentally different in their implementation, which drives their performance characteristics.

ArrayList maintains an internal array that dynamically resizes when needed. When you add elements beyond the current capacity, it creates a new array (typically 1.5x larger) and copies all elements from the old array to the new one. This means:

• Random access: O(1) time complexity through direct array indexing
• Element storage: Contiguous memory allocation
• Memory usage: Lower overhead per element (just the object reference)

LinkedList uses a doubly-linked node structure where each element contains references to the next and previous nodes. This means:

• Random access: O(n) time complexity as it must traverse from head or tail
• Element storage: Non-contiguous memory allocation
• Memory usage: Higher overhead per element (references to next/previous nodes)

As Baeldung explains, the internal mechanics of these data structures create fundamentally different performance profiles that make each suitable for different scenarios.

Performance Characteristics

The performance differences between these implementations are significant and well-documented:

According to Stack Overflow, “due to modern computer architecture, ArrayList will be significantly more efficient for nearly any possible use-case - and therefore LinkedList should be avoided except some very unique and extreme cases.”

When to Use LinkedList Over ArrayList

LinkedList is more appropriate in these specific scenarios:

1. Frequent Insertions and Deletions at Both Ends

When you need to add or remove elements from both the front and back of the list frequently, LinkedList provides O(1) operations for both ends:

// LinkedList excels for queue operations
LinkedList<String> names = new LinkedList<>();
names.addFirst("Alice");    // O(1)
names.addLast("Bob");       // O(1)
names.removeFirst();        // O(1)
names.removeLast();         // O(1)

As Alex Klimenko notes, “Use LinkedList when you need fast insertions and deletions from both ends, and random access isn’t required.”

2. Implementing Queue and Deque Operations

LinkedList implements the Deque interface, making it ideal for queue-like operations:

Queue<String> queue = new LinkedList<>();
queue.offer("First");   // Add to tail
queue.poll();          // Remove from head

3. When Memory Allocation is Not a Concern

LinkedList has higher memory overhead per element (storing next and previous references), but if you’re working with very large datasets where frequent resizing would be problematic, LinkedList might be preferable.

4. Frequent Modifications During Iteration

When you need to modify the list structure while iterating, LinkedList’s iterator.remove() operation is O(1), while ArrayList’s is O(n) due to element shifting.

When to Stick with ArrayList

ArrayList is the better choice in these common scenarios:

1. Random Access Requirements

When you frequently access elements by index, ArrayList’s O(1) access is significantly faster than LinkedList’s O(n):

// Random access - ArrayList is much faster
String name = names.get(100);  // O(1) vs O(n)

As Stack Abuse explains, “if you retrieve a lot of elements from within the list, an ArrayList is preferred.”

2. Modifications Mostly at the End

When you primarily add elements to the end of the list and occasionally remove from the end, ArrayList performs better:

// Adding to end - ArrayList excels
names.add("NewName");      // O(1) amortized
names.remove(names.size() - 1); // O(1)

3. General Purpose Use Cases

For most applications where you don’t have specific performance requirements favoring LinkedList, ArrayList is the default choice. According to Medium Java Performance, “When adding a large number of elements (over 100k), ArrayList demonstrates better performance.”

4. When Memory Efficiency Matters

ArrayList has lower memory overhead per element since it doesn’t need to store next and previous references.

Specific Use Case Examples

LinkedList Scenarios:

1. Browser History Implementation

LinkedList<String> history = new LinkedList<>();
history.addFirst(currentPage);  // Add new page to front
history.removeLast();           // Remove oldest page when limit reached
history.addLast(somePage);      // Navigate forward
history.removeLast();           // Go back

2. Undo/Redo System

LinkedList<Action> undoStack = new LinkedList<>();
undoStack.addLast(new Action());  // Add new action
undoStack.removeLast();           // Undo last action
undoStack.addFirst(redoAction);  // For redo functionality

3. Task Queue with Priority Operations

LinkedList<Task> taskQueue = new LinkedList<>();
taskQueue.addFirst(highPriorityTask);  // Add to front
taskQueue.addLast(lowPriorityTask);    // Add to end
taskQueue.removeFirst();               // Process high priority first

ArrayList Scenarios:

1. Data Processing with Random Access

ArrayList<DataRecord> records = new ArrayList<>();
// Process records by index
for (int i = 0; i < records.size(); i += 2) {
    DataRecord record = records.get(i);  // Fast random access
    // Process record
}

2. Caching System with LRU Eviction

ArrayList<CachedItem> cache = new ArrayList<>();
cache.add(newItem);              // Add to end
cache.remove(0);                // Remove least recently used (first)
cache.remove(cache.size() - 1);  // Remove least recently used (last)

3. Bulk Data Processing

ArrayList<Result> results = new ArrayList<>();
// Add many results
for (DataPoint point : dataPoints) {
    results.add(process(point));  // Fast append
}
// Process all results
for (int i = 0; i < results.size(); i++) {
    analyze(results.get(i));      // Fast index access
}

Performance Benchmarks

Real-world performance testing reveals some interesting patterns:

Small Lists (Under 50 Elements)

For small lists, ArrayList is often even faster than LinkedList for random operations due to the overhead of node management in LinkedList. As Reddit discussion indicates, “ArrayList is going to be faster than LinkedList for around 16-32 elements, simply because of the overhead of the linked list is distributed.”

Medium Lists (50-10,000 Elements)

ArrayList generally maintains its advantage for index-based operations, while LinkedList can be competitive for operations at both ends.

Large Lists (Over 10,000 Elements)

ArrayList’s performance advantage grows for most operations. As Java Performance notes, “When adding a large number of elements (over 100k), ArrayList demonstrates better performance.”

Iterator Operations

Using an Iterator.remove() operation, LinkedList outperforms ArrayList because ArrayList needs to shift all subsequent elements:

// Iterator removal - LinkedList is O(1), ArrayList is O(n)
Iterator<String> it = names.iterator();
while (it.hasNext()) {
    if (shouldRemove(it.next())) {
        it.remove();  // Much faster in LinkedList
    }
}

Best Practices

Default Choice

Always start with ArrayList unless you have a specific reason to use LinkedList:

// Default choice for most scenarios
List<String> names = new ArrayList<>();

Migration Guidelines

If you start with ArrayList and find performance issues:

1. Profile your application to identify bottlenecks
2. Consider LinkedList if you have frequent insertions/deletions at both ends
3. Test both implementations with realistic data sizes

Memory Considerations

• ArrayList: More memory-efficient, but may overallocate
• LinkedList: Higher memory overhead per element, but no wasted capacity

Thread Safety

Neither ArrayList nor LinkedList is thread-safe. For concurrent access, consider:

• Collections.synchronizedList()
• CopyOnWriteArrayList (for read-heavy scenarios)
• ConcurrentLinkedQueue (for concurrent queue operations)

Performance Optimization Tips

1. For ArrayList: Set initial capacity if you know the approximate size

   java

   List<String> names = new ArrayList<>(expectedSize);
   

2. For LinkedList: Use addFirst()/addLast() instead of add(0)/add(size())

3. For both: Use iterators instead of indexed loops when modifying during iteration

As DEV Community demonstrates through benchmarks, “in only 2 of them the ArrayList was clearly slower than LinkedList, and it was only cases at the start of the List. It was similar at the end, and in all others it was at least few times faster.”

Conclusion

1. ArrayList is the default choice for most Java applications due to its superior performance in common scenarios involving random access and end-based modifications.

2. LinkedList excels in specific scenarios requiring frequent insertions and deletions at both ends, queue operations, or when iterator-based modifications are common.

3. Performance differences are significant - ArrayList can be 10-100 times faster for random access operations, while LinkedList can be faster for structural changes at both ends.

4. Memory considerations matter - ArrayList has lower overhead per element, while LinkedList avoids array reallocation costs.

5. Profile before optimizing - measure your actual use case with realistic data sizes before making the switch, as small lists often behave differently than large ones.

For your typical List<String> names = new ArrayList<>() initialization, you’re making the right choice. Only consider LinkedList when you specifically need the performance characteristics it provides, such as frequent queue-like operations or modifications at both ends of the list.

Sources

1. When to use LinkedList over ArrayList in Java? - Stack Overflow
2. Java Interview: ArrayList vs LinkedList in Java: Internal Mechanics and Performance Comparison | by Alex Klimenko | Medium
3. Performance differences between ArrayList and LinkedList - Stack Overflow
4. Java ArrayList vs LinkedList | Baeldung
5. Difference Between ArrayList and LinkedList in Java - Code and Performance
6. Java Benchmark Adventures - ArrayList vs LinkedList - DEV Community
7. ArrayList has faster insert speed than LinkedList - Reddit
8. Performance: ArrayList vs Linked List | by Renan Schmitt | Java Performance | Medium
9. Difference between ArrayList and LinkedList in Java
10. ArrayList vs LinkedList in Java: A Deep Dive into Performance | by Thirupathi Pavan Sai | Javarevisited | Medium