- Introducing Kotlin and the Project 1:17
- Creating the Project 4:22
- The Main Function 3 questions
- Creating the Card Class 3:19
- Ch-ch-ch-changes! 3 questions
- The Card Class: Kollector's Edition 6:36
- Kard Klass 5 questions
- Finishing the Card Class 4:08
- Card Constructors 5 questions
- Making the Deck 3:23
- Stacking the Deck 3:56
- Deck Functions 3 questions
- Compacting the Deck 4:32
- Using the Deck 3:52
- Deck Masters 5 questions
Preview
Video Player
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Finishing the Card Class
4:08In this video we'll see how to add a constructor to our class and initialize our properties!
Right now, we've got our value and
our suit declared as immutable.
0:00
Which means they can never be changed
from zero and an empty string.
0:04
Let's see how to add a constructor and
use it to initialize our properties.
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In Kotlin,
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the constructor follows immediately
after the class name, check it out.
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Up here after the word Card,
let's add some parentheses,
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and then let's declare the parameters of
our constructor inside the parentheses.
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First we have value, which is an Int.
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And then we have suit, which is a String.
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And finally we have faceUp,
which is a Boolean.
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Once we've taken care of all
the parameters to our constructor,
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we can add this optional init
block below our properties.
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Whenever the constructor is called,
this init block will be called too.
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Essentially, Kotlin just separates
the constructor into two pieces.
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The parameters and
the initialization code.
1:00
An important thing to note about the
parameters of the constructor is that they
1:04
have a pretty limited scope.
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We can only use these parameters
in initializing a property or
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inside the init block.
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Anywhere else is off limits.
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So now, instead of initializing our
properties to potentially wrong values.
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Let's initialize them to the values
passed into the constructor.
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So value will equal value.
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Suit will equal suit.
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And faceUp can equal faceUp.
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Now, we don't actually need
the init block for our card class.
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But before we get rid of it,
let me show you something kind of cool.
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We know that if we don't initialize our
value property, we'll get an error.
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But we are allowed to initialize
it in the init block instead.
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This.value = value.
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All right, let's undo that and
as promised, let's delete the init block.
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Then, to get this down to one line,
we just add value or
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var in front of
the constructor parameters.
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In Kotlin, adding val or
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var in front of a constructor
parameter upgrades it into a property.
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So we can massively simplify our
code by adding val in front of
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this value parameter,
val in front of the suit parameter and
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var in front of the faceUp parameter.
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Then since we no longer need our
initial properties, let's delete them.
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And since there's nothing
inside our class,
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we can even delete the brackets too.
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While we're at it,
let's also delete the JavaCard class.
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Okay, just one more cool thing and then I
promise we'll move on from the Card class.
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So each card in the deck starts face down.
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And wouldn't it be nice if we could
have an alternate version of this
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constructor that didn't require us
to pass in the faceUp parameter?
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Well, with Kotlin,
we can specify default values for
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our parameters just by
adding an equal sign.
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So let's add =false.
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And now, we can create new facedown card
instances with just a value and a suit.
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Kotlin is an awesome language that gives
us a ton of new tools to play with.
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But that also means things can
be a bit confusing at times.
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If you're ever feeling stuck,
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there's tons of excellent
documentation at kotlinlang.org.
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Seriously, the Kotlin docs are way
better than the Android docs.
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And don't forget about
your friends at Treehouse.
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We're here to help too.
4:01
Coming up, we're going to expand from this
lonely card class into an entire deck.
4:03