Array in Java vs. Arraylist in Java — What's the Difference?
By Tayyaba Rehman — Published on January 7, 2024
An Array is a fixed-size collection of elements of the same type, while ArrayList is a resizable array implementation of the List interface.
Difference Between Array in Java and Arraylist in Java
Table of Contents
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Key Differences
Arrays in Java are static in size, meaning once you define the number of elements it can hold, it cannot be changed. An ArrayList, being a part of Java’s Collection Framework, is dynamic in size and can grow or shrink as needed.
Java Arrays are allocated on the stack if they are primitives or on the heap if they are objects, and they have a fixed length determined at the time of creation. ArrayLists are always allocated on the heap and can expand and contract dynamically at runtime.
In terms of performance, accessing an element in an Array is a constant-time operation, whereas ArrayLists may take longer due to the need to check the size and potentially resize the underlying array. Arrays are therefore preferred for long-term storage of elements where the array size doesn’t change.
Array can hold both primitives and objects, while ArrayList can only hold objects. This means that if you want to store primitive data types in an ArrayList, you need to use their wrapper classes.
While both can be iterated over using a for-loop, Array does not offer any other methods since it is not part of the Collections Framework. On the other hand, ArrayList provides methods like add(), remove(), and contains() which give it more functionality out of the box.
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Comparison Chart
Size
Fixed size
Dynamic size
Type of Data
Can hold primitives and objects
Can only hold objects
Performance
Fast element access
Slower access; may need to resize
Part of Collection Framework
No
Yes
Methods
Does not have methods besides length
Has methods like add(), remove(), etc.
Memory Allocation
On stack for primitives, heap for objects
Always on the heap
Usage
Preferred for fixed-size collections
Preferred for collections that vary in size
Compare with Definitions
Array in Java
Can store primitives or objects.
String[] names = {Alice, Bob, Charlie};
Arraylist in Java
Provides dynamic array resizing.
List.add(new item);
Array in Java
Memory efficient for fixed data.
Byte[] data = new byte[1024];
Arraylist in Java
Supports Collection Framework methods.
String item = list.get(0);
Array in Java
Fixed-size collection of elements.
Int[] numbers = new int[10];
Arraylist in Java
Resizable array implementation of List.
ArrayList list = new ArrayList<>();
Array in Java
Access to elements by index.
Double value = myArray[3];
Arraylist in Java
Can only store objects, not primitives.
ArrayList numbers = new ArrayList<>();
Array in Java
Has fixed length after creation.
Boolean[] flags = new boolean[5];
Arraylist in Java
Less memory efficient but more flexible.
List.remove(item);
Common Curiosities
What is an ArrayList in Java?
ArrayList is a resizable-array implementation of the Java List interface.
How does ArrayList handle resizing?
ArrayList automatically resizes by creating a new array and copying elements when needed.
Is there a performance advantage to using Arrays in Java?
Yes, Arrays have a performance advantage in element access and memory usage.
What is an Array in Java?
It's a container object that holds a fixed number of values of a single type.
Can Arrays in Java be multidimensional?
Yes, Java supports multidimensional arrays.
Can an Array in Java grow dynamically?
No, an Array in Java is fixed in size once it is created.
Can you store different types in a Java Array?
Only if they are subclasses of the same parent class; otherwise, use an ArrayList
What are the advantages of using an ArrayList over an Array?
ArrayList provides more flexibility with its dynamic sizing and useful methods part of the List interface.
How do you initialize an Array in Java?
By specifying the size or by initializing it with values, e.g., new int[5] or new int[]{1, 2, 3}.
What methods are unique to ArrayList in Java?
ArrayList has methods like add(), remove(), and clear() which Arrays do not have.
Are ArrayLists in Java synchronized?
No, ArrayLists are not synchronized. For thread-safe implementation, consider using Vector or Collections.synchronizedList.
Can an ArrayList in Java store primitive types?
No, it can only store objects; primitive types must be wrapped in their respective wrapper classes.
How do you add an element to an Array in Java?
You cannot add elements to an Array as it has a fixed size.
How do you convert an ArrayList to an Array in Java?
Use the toArray() method provided by the ArrayList class.
How do you iterate over an ArrayList in Java?
You can use for-each loop, iterator, or listIterator.
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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.
