Scala Tutorial - Learn How To Use Scala's Mutable ArrayBuffer

By Nadim Bahadoor | Last updated: July 25, 2017 at 14:43 pm

Overview

In this tutorial, we will learn how to use Scala's Mutable ArrayBuffer to perform common operations such as initialize an ArrayBuffer, access elements at specific index, add and remove elements and create an empty ArrayBuffer.

 

More advanced functions such as aggregate, fold, reduce, map, flatMap etc on the Mutable ArrayBuffer will be discussed in Chapter 8 on Collection Functions.

 

What is an ArrayBuffer?

As per the Scala Documentation, an ArrayBuffer is a mutable data structure which allows you to access and modify elements at specific index.

 

Compared to the previous tutorial on Array, an ArrayBuffer is resizable while an Array is fixed in size.

Steps

1. How to initialize an ArrayBuffer with 3 elements

The code below shows how to initialize an ArrayBuffer with 3 elements.


import scala.collection.mutable.ArrayBuffer
println("Step 1: How to initialize an ArrayBuffer with 3 elements")
val arrayBuffer1: ArrayBuffer[String] = ArrayBuffer("Plain Donut","Strawberry Donut","Chocolate Donut")
println(s"Elements of arrayBuffer1 = $arrayBuffer1")

You should see the following output when you run your Scala application in IntelliJ:


Step 1: How to initialize an ArrayBuffer with 3 elements
Elements of arrayBuffer1 = ArrayBuffer(Plain Donut, Strawberry Donut, Chocolate Donut)

 

2. How to access elements of an ArrayBuffer at specific index

The code below shows how to access elements of an ArrayBuffer at specific index.


println("\nStep 2: How to access elements of an ArrayBuffer at specific index")
println(s"Element at index 0 = ${arrayBuffer1(0)}")
println(s"Element at index 1 = ${arrayBuffer1(1)}")
println(s"Element at index 2 = ${arrayBuffer1(2)}")

You should see the following output when you run your Scala application in IntelliJ:


Step 2: How to access elements of an ArrayBuffer at specific index
Element at index 0 = Plain Donut
Element at index 1 = Strawberry Donut
Element at index 2 = Chocolate Donut

3. How to add elements to an ArrayBuffer using +=

The code below shows how to add elements to an ArrayBuffer using +=.


println("\nStep 3: How to add elements to an ArrayBuffer using +=")
arrayBuffer1 += "Vanilla Donut"
println(s"Elements of arrayBuffer1 = $arrayBuffer1")
// NOTE: arrayBuffer1 is mutable and hence we were able to add a new element to it

You should see the following output when you run your Scala application in IntelliJ:


Step 3: How to add elements to an ArrayBuffer using +=
Elements of arrayBuffer1 = ArrayBuffer(Plain Donut, Strawberry Donut, Chocolate Donut, Vanilla Donut)

 

4. How to add elements from a List to an ArrayBuffer using ++=

The code below shows how to add elements from a List to an ArrayBuffer using ++=.


println("\nStep 4: How to add elements from a List to an ArrayBuffer using ++=")
arrayBuffer1 ++= List[String]("Glazed Donut", "Krispy creme")
println(s"Elements of arrayBuffer1 = $arrayBuffer1")

You should see the following output when you run your Scala application in IntelliJ:

Step 4: How to add elements from a List to an ArrayBuffer using ++=
Elements of arrayBuffer1 = ArrayBuffer(Plain Donut, Strawberry Donut, Chocolate Donut, Vanilla Donut, Glazed Donut, Krispy creme)

 

5. How to remove elements from an ArrayBuffer

The code below shows how to remove elements from an ArrayBuffer.


println("\nStep 5: How to remove elements from an ArrayBuffer")
arrayBuffer1 -= "Plain Donut"
println(s"Elements of arrayBuffer1 = $arrayBuffer1")

You should see the following output when you run your Scala application in IntelliJ:

Step 5: How to remove elements from an ArrayBuffer
Elements of arrayBuffer1 = ArrayBuffer(Strawberry Donut, Chocolate Donut, Vanilla Donut, Glazed Donut, Krispy creme)

 

6. How to remove elements of a List from ArrayBuffer using --=

The code below shows how to remove elements of a List from ArrayBuffer using --=.


println("\nStep 6: How to remove elements of a List from ArrayBuffer using --=")
arrayBuffer1 --= List[String]("Glazed Donut", "Krispy creme")
println(s"Elements of arrayBuffer1 = $arrayBuffer1")

You should see the following output when you run your Scala application in IntelliJ:


Step 6: How to remove elements of a List from ArrayBuffer using --=
Elements of arrayBuffer1 = ArrayBuffer(Strawberry Donut, Chocolate Donut, Vanilla Donut)

 

7. How to initialize an empty ArrayBuffer

The code below shows how to initialize an empty ArrayBuffer.


println("\nStep 7: How to initialize an empty ArrayBuffer")
val emptyArrayBuffer: ArrayBuffer[String] = ArrayBuffer.empty[String]
println(s"Empty array buffer = $emptyArrayBuffer")

You should see the following output when you run your Scala application in IntelliJ:


Step 7: How to initialize an empty ArrayBuffer
Empty array buffer = ArrayBuffer()

 

This concludes our tutorial on Learn How To Use Scala's Mutable ArrayBuffer and I hope you've found it useful!

 

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Summary

In this tutorial, we went over the following:

  • How to initialize an ArrayBuffer with 3 elements
  • How to access elements of an ArrayBuffer at specific index
  • How to add elements to an ArrayBuffer using +=
  • How to add elements from a List to an ArrayBuffer using ++=
  • How to remove elements from an ArrayBuffer
  • How to remove elements of a List from ArrayBuffer using --=
  • How to initialize an empty ArrayBuffer

Tip

Source Code

The source code is available on the allaboutscala GitHub repository.

 

What's Next

In the next tutorial, I will show you how to use Scala's Mutable ArrayStack.

 

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Nadim Bahadoor
Senior Software Developer | Elsevier
Founder of allaboutscala.com. I have over 10 years of experience in building large scale real-time trading systems in the financial industry. Passionate about Distributed Systems, Scala, Big Data and Functional Programming. Stay in touch for upcoming tutorials!
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