In this tutorial, we will show how to use
Option
,
Some
and
None
.
If you have used other programming languages in the past such as
Java
or
.NET
, I'm pretty sure that you must have seen your share of
NullPointerException
!
By making use of
Option, Some
and
None
, Scala encourages you to write functions with no side effects as we've described in the
Scala Features tutorial
. As a result, all your headaches with
NullPointerException
should go away :)
Steps
1. How to use Option and Some - a basic example
Let's declare a simple String called
glazedDonutTaste
. But instead of its type being just a String, you will declare it as an
Option
of type String using the syntax
Option[String]
.
You can then assign its value using the
Some
class and pass in your donut taste String of
Very Tasty
.
println("Step 1: How to use Option and Some - a basic example")
val glazedDonutTaste: Option[String] = Some("Very Tasty")
println(s"Glazed Donut taste = ${glazedDonutTaste.get}")
You should see the following output when you run your Scala application in IntelliJ:
Step 1: How to use Option and Some - a basic example
Glazed Donut taste = Very Tasty
NOTE:
Because we have wrapped our String into an Option, to retrieve its value we call the
get()
function as shown above.
But calling
get()
in a production system is generally a
code smell
as you may end up with the same
NullPointerException.
2. How to use Option and None - a basic example
Let's use another variable called
glazedDonutName
which is also an
Option
of type String. But instead of initializing it to a String which is wrapped up into a
Some
class as shown in Step 1, let's set its value to
None.
println("\nStep 2: How to use Option and None - a basic example")
val glazedDonutName: Option[String] = None
println(s"Glazed Donut name = ${glazedDonutName.getOrElse("Glazed Donut")}")
You should see the following output when you run your Scala application in IntelliJ:
Step 2: How to use Option and None - a basic example
Glazed Donut name = Glazed Donut
NOTE:
We've used the handy
getOrElse()
function from the
Option
to supply a default value.
If you were to call the
get()
function as shown in Step 1, you will get the exception
java.util.NoSuchElementException: None.get
.
At this point, you may be asking yourself that this exception is similar to your
NullPointerException.
And you are absolutely right! But
Pattern Matching
is your friend :) let's look at Step 3 below.
3. How to use Pattern Matching with Option
Feel free to review the two previous tutorials
Pattern Matching
and
Tuples
.
You've already seen from Step 2 that you can use the
getOrElse()
function to get a default value in case your variable had no data.
But you can also use
Pattern Matching
as shown below:
println("\nStep 3: How to use Pattern Matching with Option")
glazedDonutName match {
case Some(name) => println(s"Received donut name = $name")
case None => println(s"No donut name was found!")
You should see the following output when you run your Scala application in IntelliJ:
Step 3: How to use Pattern Matching with Option
No donut name was found!
NOTE:
Sure, you can argue that we have not achieved much!
But, let's take a pause and assume that you were calling some
function
to populate your variable
glazedDonutName
As a consumer of that function call, you would not know that the function could potentially return null.
What have we learned? It's all about intent!
By being explicit that such a function will return an Option, any consumer of the function can avoid
NullPointerException
by using
getOfElse()
or
Pattern Matching
.
Not to worry, we will see examples of functions which return Option in upcoming tutorials.
This concludes our tutorial on
Learn How To Use Option - Avoid Null
and I hope you've found it useful!
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and
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for upcoming tutorials!
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How to use Option and Some
How to use Option and None
How to use Pattern Matching with Option
You can use the
map()
function as a more elegant way of filtering out
None
.
println("\nTip 1: Filter None using map function")
glazedDonutTaste.map(taste => println(s"glazedDonutTaste = $taste"))
glazedDonutName.map(name => println(s"glazedDonutName = $name"))
You should see the following output when you run your Scala application in IntelliJ:
Tip 1: Filter None using map function
glazedDonutTaste = Very Tasty
NOTE:
Notice that glazedDonutName was not printed as its value was None
If the map() function is completely new to you, don't worry we will see more examples when we get to the tutorials on functions.
Source Code
The source code is available on the allaboutscala GitHub repository.
What's Next
In the next tutorial, I will go over the type hierarchy in Scala.
Technology and Finance Consultant with over 14 years of hands-on experience building large scale systems in the Financial (Electronic Trading Platforms), Risk, Insurance and Life Science sectors. I am self-driven and passionate about Finance, Distributed Systems, Functional Programming, Big Data, Semantic Data (Graph) and Machine Learning.
