List in Java vs. ArrayList in Java — What's the Difference?
By Tayyaba Rehman — Published on January 5, 2024
List is an interface in Java defining a collection, while ArrayList is a resizable-array implementation of the List interface.
Difference Between List in Java and ArrayList in Java
Table of Contents
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Key Differences
A List in Java is an interface that represents a group of objects known as elements, sequenced in a linear order. The ArrayList class, however, is one specific implementation of this interface that uses a dynamic array to store the elements.
The List interface provides a blueprint for storing a sequence of elements, with methods to add, remove, and retrieve elements from this sequence. In contrast, ArrayList concretizes this blueprint with array-backed functionality, allowing for fast random access to elements but slower insertions and deletions.
Every ArrayList is a List, but not every List is an ArrayList. This is because List is abstract, allowing for different kinds of implementations like LinkedList or Vector, each with its own advantages. ArrayList is preferred for its simplicity and performance when frequent read operations are needed.
List provides the flexibility to switch between different implementations without changing much of the code structure. ArrayList provides an optimized way to manage arrays internally, automatically resizing itself when needed.
Understanding the distinction between List and ArrayList is fundamental for Java developers. While List sets the rules, ArrayList follows them, providing an optimized way to manipulate arrays of objects in memory.
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Comparison Chart
Type
Interface
Class
Implementation
Requires an implementing class
Is an implementing class
Flexibility
Can switch implementations
Fixed to array-backed implementation
Storage Mechanism
Abstract, depends on implementation
Resizable array
Method of Resizing
Implementation-dependent
Automatically resizes
Best Used For
Defining structure without implementation specifics
Fast random access operations
Compare with Definitions
List in Java
A List can be implemented by various classes like ArrayList, LinkedList, etc.
List grades = new LinkedList<>();
ArrayList in Java
Offers constant-time performance for the add operation, excluding resizing overhead.
ArrayList.add(0, element);
List in Java
It allows duplicate elements and maintains insertion order.
List numbers = Arrays.asList(1, 2, 3, 2);
ArrayList in Java
Provides a dynamic array that grows as needed.
ArrayList numbers = new ArrayList<>(30);
List in Java
It is a child interface of Collection.
List
ArrayList in Java
ArrayList is a resizable array implementation of the List interface.
ArrayList list = new ArrayList<>();
List in Java
Provides methods for positional access and search.
String firstItem = list.get(0);
ArrayList in Java
Allows fast random access to its elements.
Integer number = arrayList.get(2);
List in Java
A List is an ordered collection of elements.
List names = new ArrayList<>();
ArrayList in Java
Not synchronized, thus not thread-safe unless externally synchronized.
ArrayList synchronizedList = Collections.synchronizedList(new ArrayList());
Common Curiosities
Does ArrayList maintain the insertion order?
Yes, ArrayList maintains the order in which elements are inserted.
Can we replace ArrayList with LinkedList?
Yes, since both implement the List interface.
Are List and ArrayList synchronized?
No, both List (interface) and ArrayList are not synchronized.
Can ArrayList contain duplicate elements?
Yes, ArrayList allows duplicate elements.
Is List in Java an abstract class?
No, List is an interface, not an abstract class.
How do you remove an element from an ArrayList?
Use arrayList.remove(object) or arrayList.remove(index).
Can a List be converted back to an array?
Yes, using list.toArray(new Type[list.size()]).
Can you instantiate a List in Java?
No, you cannot instantiate a List as it is an interface.
Can ArrayList be multi-dimensional?
Yes, you can have ArrayList>.
Do List and ArrayList allow null elements?
Yes, they both allow null elements.
How do you convert an array to a List?
Use Arrays.asList(array) to convert it to a List.
How to sort an ArrayList?
Use Collections.sort(arrayList) to sort it.
What is the initial capacity of an ArrayList when created with the default constructor?
The default capacity is 10.
How to ensure thread safety with ArrayList?
Wrap it using Collections.synchronizedList(new ArrayList()).
Is it possible to create a List of primitive types?
No, use wrapper classes like Integer for List.
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Written by
Tayyaba RehmanTayyaba Rehman is a distinguished writer, currently serving as a primary contributor to askdifference.com. As a researcher in semantics and etymology, Tayyaba's passion for the complexity of languages and their distinctions has found a perfect home on the platform. Tayyaba delves into the intricacies of language, distinguishing between commonly confused words and phrases, thereby providing clarity for readers worldwide.
