Understanding the Performance Differences Between ArrayList and LinkedList in Java

What are the key performance differences between ArrayList and LinkedList in Java?

List<String> arrayList = new ArrayList<>();
arrayList.add("A");
arrayList.add("B");
arrayList.add("C");
arrayList.remove("B");
System.out.println(arrayList.get(1)); // Outputs "C"

In Java, both ArrayList and LinkedList are commonly used data structures, but their performance characteristics differ based on their underlying implementations. This article clarifies these differences, particularly in the context of random access, insertion, and deletion operations.

List<String> linkedList = new LinkedList<>();
linkedList.add("A");
linkedList.add("C");
linkedList.add(1, "B"); // Efficient insertion
System.out.println(linkedList.get(1)); // Outputs "B"

Causes

• ArrayList stores elements in a dynamic array, allowing quick access to elements via their index, while LinkedList consists of nodes that link to each other, making sequential access necessary.
• Random access time complexity for ArrayList is O(1), whereas for LinkedList it is O(n) since it may require traversing nodes from the head until the desired index is reached.
• For deletion in an ArrayList, if an element is removed, subsequent elements must be shifted to fill the gap, causing an O(n) operation, while LinkedList can simply adjust pointers, making it O(1).
• Insertion in ArrayList may require resizing the backing array, which can be costly. If inserting in the middle, subsequent elements must be shifted, resulting in O(n). In a LinkedList, insertion is O(1) once the desired position is reached.

Solutions

• Use ArrayList when frequent random access is required, as it provides fast O(1) access times for indexed elements.
• Utilize LinkedList for scenarios involving numerous insertions and deletions, particularly when these operations occur at known positions (e.g., at the start or end of the list).
• Consider the context of your application; if your usage pattern heavily incorporates deletions and insertions at unpredictable positions, opt for LinkedList. If your operations entail more reads (e.g., traversals or lookups), prefer ArrayList.

Mistake: Confusing random access speed; assuming LinkedList can access elements quickly due to its structure.

Solution: Remember that LinkedList requires traversing nodes to reach a specific index, whereas ArrayList can directly access it.

Mistake: Using LinkedList when extensive random access is needed, leading to performance issues.

Solution: Analyze your access patterns; prefer ArrayList for better performance in cases of frequent indexed access.

Mistake: Not considering resizing behavior of ArrayList during insertions, leading to underperformance in certain cases.

Solution: Plan the initial capacity of an ArrayList to minimize resizing during insertions.