Differences between ArrayList and LinkedList in Java

Learn the key differences between ArrayList and LinkedList in Java with easy examples, use cases, and best practices to master Java collections confidently.

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🧩 Introduction

Imagine you’re organizing a queue of people at a concert. Sometimes you need quick access to the fifth person in line, and other times, you just need to add or remove people from the queue efficiently. In Java programming, these real-life situations are handled by two powerful data structures — ArrayList and LinkedList.

Both are part of the Java Collections Framework, and both implement the List interface. But the way they store and manage data is very different. Understanding when to use which one can make your Java programs faster, more memory-efficient, and easier to maintain.

In this blog, you’ll learn the core differences between ArrayList and LinkedList, see practical Java code examples, and discover best practices to choose the right one for your next project.

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⚙️ Core Concepts

Before we compare them, let’s understand how they work behind the scenes.

1. ArrayList: The Dynamic Array

Think of an ArrayList like a resizable array.
It stores elements in a contiguous block of memory (like seats in a theater). If you know the position of an element, you can instantly access it — just like finding your seat by number.

• Data structure used: Dynamic array
• Access time: Very fast (O(1)) for accessing elements by index
• Insertion/deletion: Slower (O(n)) — shifting may be needed
• Memory usage: Compact, but resizing may create overhead

✅ Use when:

• You need fast random access
• You rarely insert or remove elements in the middle
• You deal with fixed or moderately changing lists

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2. LinkedList: The Chain Connection

A LinkedList, on the other hand, is like a chain of train cars — each car (called a node) holds data and a link to the next and previous cars.

• Data structure used: Doubly linked list
• Access time: Slower (O(n)) — you must traverse from the start
• Insertion/deletion: Faster (O(1)) when adding/removing from the ends or middle (with a known reference)
• Memory usage: More — due to storing extra pointers (next and previous links)

✅ Use when:

• You frequently add or remove elements
• You don’t need fast random access
• You’re implementing queues, stacks, or iterative traversals

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3. Quick Comparison Table

Feature	ArrayList	LinkedList
Data Structure	Dynamic array	Doubly linked list
Access Time (get/set)	O(1)	O(n)
Insertion/Deletion (middle)	O(n)	O(1) (if node known)
Insertion/Deletion (end)	O(1)*	O(1)
Memory Usage	Less	More (extra pointers)
Ideal Use Case	Random access	Frequent insert/delete

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💻 Code Examples (Java 21)

Example 1: Using ArrayList for Random Access

import java.util.ArrayList;

public class ArrayListExample {
    public static void main(String[] args) {
        // Create an ArrayList of fruits
        ArrayList<String> fruits = new ArrayList<>();

        // Add elements
        fruits.add("Apple");
        fruits.add("Banana");
        fruits.add("Cherry");

        // Access elements quickly using index
        System.out.println("First fruit: " + fruits.get(0));

        // Modify element
        fruits.set(1, "Blueberry");

        // Iterate over list
        System.out.println("Updated Fruits List:");
        for (String fruit : fruits) {
            System.out.println(fruit);
        }

        // Remove an element
        fruits.remove("Apple");

        System.out.println("After removal: " + fruits);
    }
}

📝 Explanation:
This program shows how ArrayList allows quick access to any element by index. However, when you remove “Apple,” the list shifts all subsequent elements, which takes extra time for large lists.

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Example 2: Using LinkedList for Frequent Insertions

import java.util.LinkedList;

public class LinkedListExample {
    public static void main(String[] args) {
        // Create a LinkedList of tasks
        LinkedList<String> tasks = new LinkedList<>();

        // Add tasks at the beginning and end
        tasks.add("Wake up");
        tasks.addLast("Brush teeth");
        tasks.addFirst("Turn off alarm");

        // Display all tasks
        System.out.println("Today's Tasks: " + tasks);

        // Remove the first task (head)
        tasks.removeFirst();

        // Add a new task in between
        tasks.add(1, "Make coffee");

        System.out.println("Updated Task List: " + tasks);
    }
}

📝 Explanation:
In a LinkedList, adding or removing elements at the start or end is very efficient. However, accessing a specific element by index takes longer since it must traverse each node sequentially.

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✅ Best Practices for Using ArrayList and LinkedList

1. Choose Based on Access Pattern:

• Use ArrayList when you need fast random access.
• Use LinkedList when frequent insertions or deletions are required.

1. Avoid Mixing Use Cases:
   Don’t use LinkedList just because it “sounds faster.” For example, if your app mostly reads data, ArrayList is better.

2. Beware of Memory Overhead:
   LinkedList consumes more memory because each element stores two extra pointers.

3. Iterate Efficiently:
   Always use enhanced for loops or iterators instead of manual index-based loops in LinkedList — it’s much more efficient.

4. Benchmark Before Deciding:
   Performance differences can depend on JVM optimizations and data size. Try both structures with real data before finalizing your choice.

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🏁 Conclusion

Both ArrayList and LinkedList are powerful tools in Java programming, but they shine in different scenarios.
If you want speedy access and less memory usage, go for ArrayList.
If you need frequent additions or deletions, LinkedList is your friend.

Understanding their differences not only improves your code’s performance but also helps you make smarter design decisions.
So next time you build a Java application, pause and think — “Am I seating people in a theater (ArrayList) or linking train cars (LinkedList)?”

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