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Software Development Executive - II
Last updated on Jun 20, 2024
Last updated on Jun 20, 2024
Welcome to this comprehensive exploration of Kotlin ArrayList!
If you’re passionate about Kotlin – a cutting-edge programming language from JetBrains, you’re probably aware of the ArrayList class, a fundamental element in the Kotlin ecosystem.
This blog will unravel every nook and corner of Kotlin ArrayList, walking you through various features, operations, and usages.
An ArrayList is a resizable array, also known as a dynamic array. Unlike a traditional array that is static, ArrayList can expand or shrink dynamically as you add or remove elements. This flexibility makes working with data more efficient and reduces memory usage.
Consider this example:
1val arrayList = ArrayList<String>()
The above code snippet creates an empty ArrayList of the string type. It can accommodate any number of elements and grows accordingly.
ArrayList is widely used in Kotlin, especially in Android app development, where dealing with dynamic data sets is a daily affair. Moreover, the ArrayList class makes it significantly easier to handle sophisticated data manipulation tasks.
Consider another example:
1val arrayList = ArrayList<String>() 2arrayList.add("Kotlin") 3arrayList.add("ArrayList") 4println(arrayList)
In the above code, we first create an ArrayList and then add the string elements “Kotlin” and “ArrayList” using the add() method. The output will be [Kotlin, ArrayList]. This demonstrates how an ArrayList can be used to store and manipulate strings, making it a dynamic array string.
Understanding how the ArrayList in Kotlin operates is crucial for any Kotlin programmer. At its core, an ArrayList is a class that's a part of Kotlin's standard library and provides capabilities to create a dynamic array. Unlike fixed-sized arrays, ArrayLists grow automatically when additional elements are added.
As we have already established, an ArrayList in Kotlin is a class and it serves as a dynamic array. But what does that mean exactly? Kotlin’s ArrayList class inherits the MutableList interface. An ArrayList keeps its elements in a backing storage array. The size of this backing storage array indicates the ArrayList’s capacity.
Let’s look at an example:
1val arrayList: ArrayList<String> = ArrayList<String>() 2arrayList.add("Kotlin") 3arrayList.add("ArrayList") 4println(arrayList)
In this example, we’ve created an ArrayList and added two elements to it. When we print the content of the ArrayList, the output will be [Kotlin, ArrayList]. Note that the ArrayList can hold the elements and adjust its size as per the elements passed onto it. The ‘toString’ method provides a string representation of the ArrayList.
An ArrayList in Kotlin essentially adapts the Array type structure but is mutable, along with an ability to accommodate or drop elements, making it incredibly flexible. The ArrayList has an initial capacity, which is the size of the backing storage array. When we need more room in the ArrayList to fit the current collection of elements, the capacity is doubled.
Let's take a peek at an instance of ArrayList:
1val stringArrayList = arrayListOf<String>() 2println(stringArrayList.count())
In this example, an empty ArrayList of type String is created. Note that in Kotlin, the default initial capacity of an ArrayList is ten. However, capacity shouldn't be mistaken for the size of the ArrayList. The size corresponds to the number of elements present in the ArrayList.
Creating an ArrayList in Kotlin is as straightforward as it gets. You can create either an empty ArrayList or an ArrayList filled with elements:
1val stringArrayList = arrayListOf<String>() 2val listOfNumbers = arrayListOf(1, 2, 3, 4, 5)
In the first line, an empty ArrayList of type String is created. In the second line, an ArrayList named listOfNumbers is created with the values 1 to 5.
Once the ArrayList is created in Kotlin, you'd want to manipulate all the elements it contains. Let's dive a bit deeper into these aspects of Kotlin ArrayLists.
The ‘add’ function in Kotlin ArrayList helps you add elements to the ArrayList. ArrayList provides us the flexibility to add elements at the end, at a particular index, or even add all the elements of another collection!
1val stringsArrayList: ArrayList<String> = ArrayList() 2stringsArrayList.add("Hello") 3stringsArrayList.add("World") 4stringsArrayList.add(1,"Kotlin")
In this snippet, we’re adding the string “Hello” and “World” to our ArrayList. The add() method returns a boolean indicating a successful addition. The “Kotlin” string has been added at index int 1.
The add() function can also add a collection of elements:
1val firstArrayList: ArrayList<String> = ArrayList() 2val secondArrayList: ArrayList<String> = ArrayList() 3 4secondArrayList.add("Element1") 5secondArrayList.add("Element2") 6 7firstArrayList.addAll(secondArrayList)
In this case, the addAll() method appends all the elements from secondArrayList to firstArrayList.
Just as adding elements, removing elements is also an essential operation offered by Kotlin ArrayList. The ArrayList class provides you with multiple methods to remove elements:
1val arrayList = arrayListOf("Element1", "Element2", "Element3") 2arrayList.remove("Element2")
In this snippet, the remove() function deletes the first occurrence of "Element2". If the removal is successful, the function returns true else false.
To remove all the elements in the ArrayList, you can use clear():
1val arrayList = arrayListOf("Element1", "Element2", "Element3") 2arrayList.clear()
The above code snippet will clear all elements from the ArrayList.
You can access elements in the ArrayList using the get() function, which requires an index as a parameter:
1val arrayList = arrayListOf("Element1", "Element2", "Element3") 2println(arrayList[0]) // prints "Element1" 3println(arrayList.get(1)) // prints "Element2"
The ArrayList class provides a set of methods for modifying elements at a specific position.
There are circumstances when you need to modify a particular element at a specific position. You can modify the elements of an ArrayList using the set() function:
1val stringsArrayList: ArrayList<String> = ArrayList() 2stringsArrayList.add("Hello") 3stringsArrayList.add("World") 4stringsArrayList.add("Kotlin") 5stringsArrayList.set(2, "ArrayList") // sets the element at index 2 to "ArrayList"
In this snippet, we first add the elements “Hello”, “World”, and “Kotlin” to our ArrayList. After that, we replace the third element “Kotlin” with “ArrayList” using the set() function.
Modifying an element in a list may affect its adjacent elements, especially in data structures like LinkedLists where elements are linked with pointers.
The set() function is used to update an element at a specific position in the ArrayList. It takes two parameters an index and the element to be stored at that index. The function replaces the current element at the specific index with the specified element.
Let's revise this with an example:
1val stringsArrayList: ArrayList<String> = ArrayList() 2stringsArrayList.add("Kotlin") 3stringsArrayList.add("Hello") 4stringsArrayList.set(0, "Hi") // sets the element at index 0 to "Hi"
Now, when you print your ArrayList, the output will be: [Hi, Hello] – the first element "Kotlin" has been replaced by "Hi".
One of the primary strengths of Kotlin ArrayList is its interoperability with Java collections. It blends well with other collections and offers a range of functionalities to manipulate data.
In Kotlin, collections are a robust way of dealing with a set of data. Be it a list of numbers, a list of strings, or a list of custom objects, collections find their place everywhere. They are primarily categorized into two types – immutable collection (read-only) and mutable collection (read and write). Understanding how to effectively employ Kotlin collections is crucial to be productive with the language.
An ArrayList is a part of the collection. It's a mutable collection to be precise, which means you can perform read/write operations on it. The ArrayList class inherits continuity from the Collection interface in Java. As a result, you can use all the functions of Java Collection with ArrayList in your Kotlin program.
1val arrayList = arrayListOf(1, 2, 3, 4, 5) 2println(arrayList.sum())
Here, the sum() function is a part of the Collection functions and returns the sum of all elements in the ArrayList.
An ArrayList in Kotlin can easily adapt to a specified collection. Let's look at an example:
1val numbersArrayList = arrayListOf(1, 2, 3, 4, 5) 2val stringsArrayList = arrayListOf("One", "Two", "Three", "Four", "Five") 3val mixedList = arrayListOf<Any>() 4 5mixedList.addAll(numbersArrayList) 6mixedList.addAll(stringsArrayList) 7 8println(mixedList)
In this example, we create an ArrayList of integers, an ArrayList of strings, and a mixedList of type Any. We then add all elements of numbersArrayList and stringsArrayList to mixedList. The output will be [1, 2, 3, 4, 5, One, Two, Three, Four, Five].
In Kotlin, array indexes are essential. An index denotes the position of an element in the array list. It starts from zero which means the first element is located at index zero, the second at index one, and so forth.
Indexes are integer values representing the position of a specific element in the Kotlin ArrayList. It enables us to access, modify, and remove elements according to their positions. Below is a simple way to create and access elements using indexes:
1val numbersArrayList = arrayListOf(1, 2, 3, 4, 5) 2println(numbersArrayList[1]) // prints "2"
In the above snippet, we are accessing the second element located at index one in the numbersArrayList.
An index plays a significant role in Kotlin ArrayLists. With the use of indexes, you can perform various operations such as adding, updating, and removing elements at specified positions:
1val stringArrayList = arrayListOf("Hello", "World", "Kotlin") 2stringArrayList.add(1, "Programming") 3println(stringArrayList) // prints [Hello, Programming, World, Kotlin]
In this snippet, we inserted the String “Programming” at index 1. Hence, the output now shows “Programming” in the second position. Inserting an element at a specified position will shift the two adjacent elements accordingly.
On the other hand, in an operation involving deletion:
1val stringArrayList = arrayListOf("Hello", "World", "Kotlin") 2stringArrayList.removeAt(1) 3println(stringArrayList) // prints [Hello, Kotlin]
Here, we are removing the element located at index 1 which is “World”. The output confirms the deletion.
While using indexes, we must be cognizant of the IndexOutOfBoundsException. It occurs when we reference an index that is beyond the ArrayList's size.
1val stringsArrayList = arrayListOf("Hello", "World") 2println(stringsArrayList[3]) // throws an IndexOutOfBoundsException
In the above, we attempted to reference the non-existent 4th element from an ArrayList of size 2, resulting in Kotlin throwing an IndexOutOfBoundsException.
Whenever we manipulate an ArrayList using an index, we should ensure the index is within the valid range.
The ability to transform one type of collection into another is among the strengths of collection classes in Kotlin. Transformation helps couple your code with meaningful and powerful conversions.
To convert a Kotlin List to an ArrayList, we can simply use the toArrayList() function. This function lets us create a new ArrayList initialized with the elements of the current list.
Let's explore this with an example:
1val list = listOf("One", "Two", "Three") 2val arrayList = ArrayList(list) 3println(arrayList) // prints [One, Two, Three]
In the above code snippet, we first create a list and then convert the list to an ArrayList. On printing, we can see that all the elements of the list are copied to the ArrayList.
In terms of advantages, flexible size, and manipulations are the primary ones. Arrays in Kotlin have a fixed size, whereas ArrayLists can grow or shrink dynamically.
However, a minor downside of using an ArrayList instead of an array is that they generally consume more memory due to their dynamic nature.
Just as we transformed Kotlin List to ArrayList, there's a provision for the vice versa operation – Converting a Kotlin Array to List. It's just as straightforward.
Kotlin provides helpful built-in functions, which make the transition from array to list seamless. The toTypedArray() function transforms the List to an Array, while the toList() function helps convert an Array to List.
Here's an example illustrating the transformation of Kotlin Array to List:
1val array = arrayOf("One", "Two", "Three") 2val list = array.toList() 3println(list) // prints [One, Two, Three]
In the code above, we initially declare an array with elements "One", "Two", and "Three". We then invoke the toList() method to convert the array into a list.
Conversion between array and list is commonly used in Kotlin, particularly when Android developers are switching between Java and Kotlin. Since Java uses arrays more frequently and Kotlin prefers lists, conversions often come into the scene when working with Android APIs.
We hope this comprehensive guide on Kotlin ArrayList has equipped you with the necessary knowledge to build effective and efficient Kotlin applications.
Indeed, the Kotlin ArrayList presents a powerful tool to handle dynamic collections - with features such as auto-resizable capacity, user-friendly functions like add(), remove(), and get(), and support for transforming other collections.
We started with the basic understanding of Kotlin ArrayList, then dove into managing elements, specifically targeting elements and collections, a detailed peek into index handling, and maneuvering Kotlin ArrayList with other frequently utilized collections like lists and arrays.
Remember these useful points:
• ArrayList is dynamically sized arrays offering more flexibility.
• An ArrayList's size is mutable, while an Array has fixed size.
• Be wary of IndexOutOfBoundsException while using get() and set().
• ArrayList's addAll() function allows to add all the elements of a specific collection.
• Functions like clear(), remove(), toList(), and many others, make manipulation of ArrayList easier.
Throughout this exploration, we understood that ArrayLists are mutable collections that offer dynamic arrays. It's possible to index, add, remove, and modify elements in an ArrayList.
Here are some crucial tips:
Always check if an index is within the valid range before trying to fetch, update, or delete an item at a particular index from an ArrayList.
While transforming one collection type to another, always ensure to assign it to an appropriate variable type to avoid ClassCastException at runtime.
While ArrayLists prove handy in most cases, be cautious when performance is your priority. The frequent resizing operation in ArrayLists can make them more CPU and memory-intensive compared to Arrays.
We have walked the journey of understanding the Kotlin ArrayList, covering critical aspects from the fundamentals to more advanced concepts like interoperability with other collections, and converting array to list and vice versa.
Throughout this exploration, you've witnessed how Kotlin ArrayList unleashes powerful functionalities that make Kotlin stand out, particularly when it comes to handling dynamic data sets. The ArrayList in Kotlin provides not just the means to house data, but also equips you with tremendous capabilities to manipulate it efficiently.
Keep quenching your knowledge thirst and keep coding! Happy Kotlin-ing!
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