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Build a Simple Android App with Kotlin

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Simple Refactoring: Using a New Class

3:47 with Ben Deitch

We have a new object in our project; let's see how to use it in our existing code!

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    First, we need to instantiate a fact book object. 0:00
    We'll do it similarly to how we created a new random object in the fact book class. 0:03
    We'll use this new fact book object to do the work of getting us a random fact 0:08
    when the button is clicked. 0:12
    We create it here in the on click method. 0:14
    But if we do that, 0:17
    a new fact book object would be created every time we tap on the button. 0:18
    That doesn't seem very efficient. 0:23
    What if our object was huge, with thousands of facts to choose from? 0:24
    On each tap, 0:28
    we'd be wasting tons of processing time just in recreating the fact book. 0:29
    Instead, let's create it just once as a property. 0:34
    Up here before the on create method but after we define our class, 0:38
    let's add some space and type private val, and name it factbook. 0:42
    And notice that we're using the private keyword word. 0:50
    We only want this variable to be available inside this class. 0:52
    No other code outside our activity needs to know about it. 0:57
    Next we need to initialize our fact book. 1:01
    Type equals capital, 1:03
    capital F, A, and then use autocomplete to finish it. 1:08
    And finally, add the parenthesis. 1:13
    This creates a new fact book object using the default constructor. 1:16
    But wait, we didn't add a constructor to our fact book class. 1:21
    And luckily, we don't need to. 1:24
    If we don't provide our own constructor, 1:26
    Catlin will automatically create one behind the scenes. 1:28
    So even if we don't add a constructor to a class, 1:32
    we can always create objects from that class by using the default constructor. 1:34
    Back in our own quick listener, let's get a random fact from our fact book object 1:40
    and store it in a variable name fact. 1:44
    Type vowel, fact, and 1:47
    set it equal to fac, book, dot and cool. 1:50
    Our gift fact method is right at the top of auto complete. 1:55
    But where did the rest of these methods come from? 1:58
    The ones we didn't write? 2:00
    In Catlin, every class either directly or indirectly extends from the any class. 2:02
    Even though we didn't use the extends keyword when writing our factBook class, 2:09
    it still extends the any class by default. 2:12
    So these other methods come from the any class. 2:15
    Let's hit Enter, and we're done. 2:18
    Now let's take a quick review of our code. 2:21
    We create our activity, and give it the layout we'd like it to display. 2:23
    Then we initialize our view variables to the views in the layout 2:27
    by using their IDs. 2:30
    Then we set an on click listener for our button, and when the button is tapped, 2:32
    we use our fact book object to get a random fact and update the fact text view. 2:36
    This looks pretty good, but let's take one more pass at our fact book class. 2:41
    First we see one of the main problems with using comments. 2:46
    We ideally want to write code that's easy to understand without additional comments. 2:50
    Comments tend to be forgotten about after they're first written and 2:54
    can end up in not making any sense. 2:57
    Like this one, let's delete it. 3:00
    All right there's one more thing we should change here, can you guess what it is? 3:04
    One of the properties of our fact book is all the facts it contains, so 3:09
    this facts array should really be a property of our fact book and 3:13
    not a local variable of the get fact method. 3:17
    Let's cut the facts declaration from the get getFact method and 3:20
    then paste it up here under Properties. 3:25
    Awesome, now it's time to test the app. 3:30
    Remember, the goal of refactoring is to make changes to the code 3:34
    without changing the behavior of the app. 3:37
    So it should work exactly the same as before. 3:40
    Great work. 3:45

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