java array length vs size

Difference between size and length methods?

stackoverflow.com › questions › 20192843 › difference-between-size-and-length-methods

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 Overflow

Stack Overflow

stackoverflow.com › questions › 20192843 › difference-between-size-and-length-methods

java - Difference between size and length methods? - Stack Overflow

Top answer

1 of 7

104

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

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.

java - Difference between size and length methods?

java - When to use .length vs .length()

java - How to resolve method length()

java - When to use length and when to use length()

java - Is there a rule of thumb for using Size or Length?

More results from stackoverflow.com

Study.com

study.com › business courses › business 104: information systems and computer applications

Java Array Length vs. Size - Video | Study.com

January 15, 2019 - The video lesson explains that ... property (e.g., array.length). ... It's important to note that "size" applies to ArrayLists, while "length" applies to arrays....

Discussions

[Java] size vs. length

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. More on reddit.com

r/learnprogramming

July 16, 2013

x.length, x.length(), or length(x)?

So len(x) is not an object-oriented approach. It's possible that it's part of an object-oriented language (and there are various reasons why you might do this), but that specific function isn't written in "an object-oriented way." Python in general doesn't seem to be quite sure whether or not it wants to be object-oriented. In ruby x.length and x.length() are the same thing: parens are optional on functions that accept no arguments. This is because in ruby you access object properties using hash notation (x[:length]). In Java x.length is a property while x.length() is a method call. The reason why it might be done this way really comes down to the decisions made when implementing the class. In Java's case, x.length() is the "more Java-y" way of doing it, but arrays use x.length because they're primitive types (although they're also objects) and thus lie in a sort of weird boundary between the object-oriented part of the language and the underlying machine details. Basically: you've stumbled into a weird edge case that exists for complicated reasons. More on reddit.com

r/learnprogramming

September 16, 2021

Why is getting the length of an array O(1) and not O(n)?

Most implementations store the length of an array in the object itself. Whenever you insert/remove it gets updated. Thus you're not iterating to get the length you're just getting a value. More on reddit.com

r/learnprogramming

November 7, 2022

Kotlin collections - Difference between size and count()?

From "Kotlin in Action" book:

SIDEBAR

"Using the right function for the job: count vs. size

It’s extremely easy to forget about count and implement it by filtering the collection and getting its size:

println(people.filter(canBeInClub27).size)

1

But in this case, an intermediate collection is created to store all the elements that satisfy the predicate. On the other hand, the count method only tracks the number of matching elements, not the elements themselves, and is therefore more efficient. As a general rule, try to find the most appropriate operation that satisfies your needs."

Top answer

1 of 3

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

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.

TheServerSide

theserverside.com › blog › Coffee-Talk-Java-News-Stories-and-Opinions › Java-length-vs-length-Whats-the-difference

Java length vs length(): What's the difference?

... The key difference between an array’s length field and Java’s length() method is that the array length field describes the size of an array, while Java’s length() method tells you how many characters a text String contains.

Published: February 3, 2026

Find elsewhere

Google Bing Mojeek

JanBask Training

janbasktraining.com › community › java › arraysize-vs-arraylength

Array.size() vs Array.length | JanBask Training Community

August 24, 2025 - Array.size() (or simply .size) returns the total number of elements currently present in the array. It’s basically the same as .length in Ruby, as both are interchangeable. ... In Java, you’ll always use .length for arrays and .size() for ...

Medium

medium.com › javarevisited › understanding-java-arrays-from-basics-to-length-and-limits-9c30f749f2fd

Understanding Java Arrays: From Basics to Length and Limits | by sajith dilshan | Javarevisited | Medium

August 25, 2025 - Array .length vs String .length(): Arrays → .length, Strings → .length(). Updating: Array size is fixed, but you can always replace elements inside. Loops: Arrays pair perfectly with loops for efficient data handling. Once you’re comfortable with arrays, you’ll find it much easier to transition to flexible collections like ArrayList, which can grow and shrink as needed. ... Follow me for more bite-sized Java tips and dev insights.

Delft Stack

delftstack.com › home › howto › java › size vs length in java

The Difference Between Size and Length in Java | Delft Stack

October 12, 2023 - Unlike the length property of arrays, the value returned by the size() method is not constant and changes according to the number of elements. All the collections of the Collection Framework in Java are dynamically allocated, so the number of ...

Quora

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

Answer (1 of 7): The length property of an array specifies the number of elements the array is capable of storing. That is it specifies the number of slots present in the array. For example, let us define an array like this:- int [] arr = new int[10]; Now when we say, arr.length, it gives us th...

Java67

java67.com › 2014 › 04 › array-length-vs-arraylist-size-java.html

Array length vs ArrayList Size in Java [Example] | Java67

I have mentioned this before on ... well. So, use length attribute to get number of elements in a array, also known as length, and for same thing in Collection classes like ArrayList, Vector, use size() method....

Quora

quora.com › What-is-the-difference-between-length-and-size-in-Java

What is the difference between length and size in Java? - Quora

Answer (1 of 4): * In java size is method which is written as size() which is available for collections. size() returns number of elements which is contain by collection (not the capacity). * where as .length is a field which works with arrays and gives capacity of arrays. * also length is a m...

GeeksforGeeks

geeksforgeeks.org › java › length-vs-length-java

length vs length() in Java - GeeksforGeeks

January 4, 2025 - Java Collection · Last Updated : 4 Jan, 2025 · array.length: length is a final variable applicable for arrays. With the help of the length variable, we can obtain the size of the array. string.length() : length() method is a final method which ...

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?

July 30, 2019 - JavaObject Oriented ProgrammingProgramming · 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 space allocated during ...

codelessgenie

codelessgenie.com › blog › difference-between-size-and-length-methods

Difference Between size() and length in Java: Array vs ArrayList Methods Explained — CodeLessGenie.com

ArrayList is a resizable, dynamic array implementation of the List interface in Java’s Collections Framework. Unlike arrays, ArrayList can grow or shrink in size automatically as elements are added or removed.

javaspring

javaspring.net › blog › java-length-vs-size

Java `length` vs `size()`: A Comprehensive Guide — javaspring.net

For example, if you create an array of integers with a length of 5, it will always have space for exactly 5 elements. The size() method is a method provided by the java.util.Collection interface and its subinterfaces and implementations. It returns the number of elements currently present in a collection.

CodeAhoy

codeahoy.com › java › array-length

Array Length in Java with Examples | CodeAhoy

January 26, 2020 - The length variable is declared as final because the length of an array is defined only when it is created and cannot be changed later. You can safely use the length field everywhere without worrying about changing it inadvertently. length vs size(): size() is a method which is defined in java.ut...

Quora

quora.com › What-is-the-difference-between-array-size-and-array-length

What is the difference between array size and array length? - Quora

Answer (1 of 4): * “Length” is generally taken to mean the number of elements in the array. * “Size” is the number of bytes that the array occupies in memory - and C provides a built-in function to return it, called “sizeof()”: EXAMPLE: [code]char array1 [ 100 ] ; int array2 [ 100 ...