size() is a method specified in java.util.Collection, which is then inherited by every data structure in the standard library. length is a field on any array (arrays are objects, you just don't see the class normally), and length() is a method on java.lang.String, which is just a thin wrapper on a char[] anyway.
Perhaps by design, Strings are immutable, and all of the top-level Collection subclasses are mutable. So where you see "length" you know that's constant, and where you see "size" it isn't.
Answer from MattPutnam on Stack OverflowQuora
quora.com › What-is-the-difference-between-length-of-array-and-size-of-ArrayList-in-Java
What is the difference between length() of array and size() of ArrayList in Java? - Quora
... Array has length function, which provides the length of the Array or Array object... The java ArrayList has size() function for ArrayList which provides the total number of objects available in the collection…
GeeksforGeeks
geeksforgeeks.org › java › difference-between-length-of-array-and-size-of-arraylist-in-java
Difference between length of Array and size of ArrayList in Java - GeeksforGeeks
July 11, 2025 - Array is static so when we create an array of size n then n blocks are created of array type and JVM initializes every block by default value. Let's see this in the following figure. On the other hand, java ArrayList does not have length property.
Top answer 1 of 7
103
size() is a method specified in java.util.Collection, which is then inherited by every data structure in the standard library. length is a field on any array (arrays are objects, you just don't see the class normally), and length() is a method on java.lang.String, which is just a thin wrapper on a char[] anyway.
Perhaps by design, Strings are immutable, and all of the top-level Collection subclasses are mutable. So where you see "length" you know that's constant, and where you see "size" it isn't.
2 of 7
48
length is constant which is used to find out the array storing capacity not the number of elements in the array
Example:
int[] a = new int[5]
a.length always returns 5, which is called the capacity of an array. But
number of elements in the array is called size
Example:
int[] a = new int[5]
a[0] = 10
Here the size would be 1, but a.length is still 5. Mind that there is no actual property or method called size on an array so you can't just call a.size or a.size() to get the value 1.
The size() method is available for collections, length works with arrays in Java.
TheServerSide
theserverside.com › blog › Coffee-Talk-Java-News-Stories-and-Opinions › Java-array-size-explained-by-example
Java array size, length and loop examples
However, Java arrays do not have a size() method, nor do they have a length() method. Instead, the property length provides a Java array’s size. To further confuse matters, every Java collection class that implements the List interface does ...
BeginnersBook
beginnersbook.com › 2022 › 08 › difference-between-length-of-array-and-size-of-arraylist-in-java
Difference between length of Array and size of ArrayList in Java
We are printing the size of array using length property and size of ArrayList using size() method. The important point to note is: If an array is defined with size 10 like this String arr[] = new String[10]; but we are only adding four elements. The length property for this array would return ...
TutorialsPoint
tutorialspoint.com › What-is-the-difference-between-the-size-of-ArrayList-and-length-of-Array-in-Java
What is the difference between the size of ArrayList and length of Array in Java?
ArrayList doesn't have length() method, the size() method of ArrayList provides the number of objects available in the collection. Array has length property which provides the length or capacity of the Array. It is the total spac
Javatpoint
javatpoint.com › difference-between-length-of-array-and-size-of-arraylist-in-java
Difference between Length of Array and Size of ArrayList in Java - javatpoint
Difference between Length of Array and Size of ArrayList in Java with list, set, map, queue, arraylist, linkedlist, hashset, linkedhashset, treeset, hashmap, linkedhashmap, storing and fetching data etc.
Java67
java67.com › 2014 › 04 › array-length-vs-arraylist-size-java.html
Array length vs ArrayList Size in Java [Example] | Java67
So next time don't confuse between length and size(), array are special object in Java and has attribute called length, which specifies number of buckets in array, while ArrayList is a Collection class, which inherit size() method, which returns number of elements inside Collection...
TutorialsPoint
tutorialspoint.com › difference-between-length-of-array-and-size-of-arraylist-in-java
Difference between length of Array and size of ArrayList in Java
Also during initialization what ... every block by a default value. On the other hand, ArrayList does not have length method but it has method named as size for calculating a number of elements get stored in it....
BeginnersBook
beginnersbook.com › 2013 › 12 › how-to-find-length-of-arraylist-in-java
How to find length of ArrayList in Java
Initial size: 0 Size after few additions: 5 Size after remove operations: 3 Final ArrayList: 1 45 99
Sarthaks eConnect
sarthaks.com › 2434808 › what-is-the-difference-between-length-and-size-of-arraylist
What is the difference between length() and size() of ArrayList? - Sarthaks eConnect | Largest Online Education Community
What is the difference between length() and size() of ArrayList? (a) length() and size() ... returns the actual number of elements stored in the list
Reddit
reddit.com › r/learnprogramming › in java, why is there no standard method for finding the size/length of different collections?
r/learnprogramming on Reddit: In Java, why is there no standard method for finding the size/length of different collections?
November 28, 2015 -
For an array, it's array.length. For strings, it's string.length(), and for arraylists, it's arraylist.size().
Is there any reason that there isn't uniformity in syntax here?
Top answer 1 of 5
35
Is there any reason that there isn't uniformity in syntax here? Screw ups when the language was designed. That's pretty much it. It's something you get used to in no time anyway so it's not that big a deal other than it's slightly annoying that they're not consistent.
2 of 5
8
I guess as arraylists can increase in size after creation, while strings and plain arrays cant (one contigious block of memory is allocated on creation - when you edit a string, you are actually creating a new one).
How to do in Java
howtodoinjava.com › home › collections framework › java arraylist › java arraylist length and size
Java ArrayList Length and Size
August 4, 2023 - ... The Java ArrayList class does not expose the length of the backing array for simplicity purposes and only exposes the count of currently stored elements in it with the size() method.
Tpoint Tech
tpointtech.com › difference-between-length-of-array-and-size-of-arraylist-in-java
Difference between length of array and size() of ArrayList in Java - Tpoint Tech
March 17, 2025 - In Java, Array and ArrayList are two different entities. In Java, and are used to determine the number of elements in different types of data structures.
Gitbooks
codehs.gitbooks.io › apjava › content › Data-Structures › arrays-vs-arraylists.html
Arrays vs ArrayLists · AP Computer Science in Java
How we retrieve the size or length of an Array or ArrayList varies between the two. When dealing with an Array we use arr.length to access its length. With ArrayLists we would use list.size(). Settings values at a given index varies as well. To set the value of a given index with an Array we use arr[i] = x;. To set the value of a given index with an ArrayList we use list.set(i, x);. To retrieve values at a given index is as follows: To get a value at a given index with an Array we use int x = arr[i];.
W3Schools
w3schools.com › java › ref_arraylist_size.asp
Java ArrayList size() Method
Arrays Loop Through an Array Real-Life Examples Multidimensional Arrays Code Challenge · Java Methods Java Method Challenge Java Method Parameters
Reddit
reddit.com › r/learnprogramming › [java] size vs. length
r/learnprogramming on Reddit: [Java] size vs. length
July 16, 2013 -
What is the reasoning behind why some objects use size() and some use length(). Why don't they all use one or the other?
Top answer 1 of 3
2
Arrays are fixed length so they use a field/variable that gets set on initialization. Lists are variable length so they need a method to figure out their own size.
2 of 3
2
I think it's only arrays that use length (not length()). Everything else that I can think of uses "size()". Arrays are weird. They are objects, but they are implemented directly in the language and not via a library. The have members (like clone() and length), but you can't access them via reflection. Personally, I think the authors of Java just made a mistake. They probably should have made it be size(), for consistency with the other containers. I'm not sure if there is a good reason why they didn't. It's just something you have to get used to.
JanBask Training
janbasktraining.com › community › java › arraysize-vs-arraylength
Array.size() vs Array.length | JanBask Training Community
August 24, 2025 - Array.length is used to get the fixed number of elements in an array. Since arrays in Java are of fixed size, this property tells you how many elements the array can hold.
Baeldung
baeldung.com › home › java › java array › the capacity of an arraylist vs the size of an array in java
The Capacity of an ArrayList vs the Size of an Array in Java | Baeldung
November 11, 2025 - We’ll also look at examples of when we should initialize ArrayList with a capacity and the benefits and disadvantages in terms of memory usage. To understand the differences, let’s first try both options. In java, it’s mandatory to specify the size of an array while creating a new instance of it: Integer[] array = new Integer[100]; System.out.println("Size of an array:" + array.length);