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Build a Simple Android App with Java

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Simple Refactoring: Using a New Class

6:28 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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    Let's go back to fun facts activity and use this new method. 0:00
    First, we need to instantiate a fact book object. 0:04
    We'll do it similarly to how we created a new OnClickListener down here or 0:08
    a new random object in the fact book class. 0:12
    We'll use this new fact book object to do the work of getting us a random fact 0:15
    when the button is clicked. 0:19
    We could create it here, in the OnClick method. 0:21
    But if we do that, 0:24
    a new fact book object would be created every time we tap on the button. 0:25
    That doesn't seem very efficient. 0:30
    What if our object was huge, with thousands of facts to choose from? 0:32
    On each tap, 0:36
    we'd be wasting tons of processing time, just in recreating the fact book. 0:37
    Instead, let's create it just once, as a field, or member variable. 0:41
    Up here before the onCreate method, but after we define our class, 0:46
    let's add some space, and type private FactBook, with a capital F. 0:51
    And then let's name it factBook. 0:58
    Which if we type a lowercase f, Android Studio will recommend for 1:00
    us, and finally, a semicolon. 1:04
    Notice we're using the class we just created as the data type for 1:08
    this variable. 1:12
    We're also using the private keyword because we only want this variable 1:14
    to be available inside this class. 1:18
    No other codes outside our activities need to know about it. 1:22
    Next we need to initialize it. 1:25
    Before the semi colon type equals new F and 1:27
    use the auto complete to finish it. 1:32
    Auto complete even adds the parenthesis to the end. 1:37
    This creates a new FactBook object using the default constructor, but wait, we 1:40
    didn't have a constructor to our FactBook class, and luckily we don't need to. 1:45
    If we don't provide our own constructor, 1:50
    Java will automatically create one behind the scenes. 1:52
    So even if we don't add a constructor to our class, 1:56
    we can always create new objects from that class by using the default constructor. 1:59
    New, then the class name, and then an empty set of parentheses. 2:04
    Back in the on-click method, lets get a random fact from our fact book object and 2:08
    store it in a variable named fact. 2:14
    Type String, fact, and 2:16
    set it equal to factBook.cool. 2:19
    Our get fact method is right at the top of auto complete. 2:24
    But where did the rest of these methods come from, the ones we didn't write? 2:27
    In java every single class either directly or indirectly extends the object class. 2:32
    Even though we didn't use the extends keyword when writing our FactBook class, 2:38
    it still extends the object class by default. 2:42
    So these other methods come from the object class. 2:45
    Let's hit Enter, then add a semicolon, and we're done. 2:49
    Now let's take a quick review of our code. 2:54
    We create our activity and give it the layout we'd like it to display. 2:57
    Then we initialize our view variables to the views in the layout 3:01
    by using their ids. 3:05
    Then we create an onClickListener for our button and when the button is tapped 3:07
    we use our FactBook object to get a random fact and update the factTextView. 3:11
    Finally, we attach our on click listener to our button. 3:16
    This looks pretty good, but let's take one more pass at our fact book class. 3:19
    First, we see one of the main problems with using comments. 3:25
    We ideally what to write a code that is easy to understand with 3:29
    out additional comments. 3:32
    Comments tend to be forgotten about after they are first written and 3:34
    can end up not making any sense. 3:37
    Like this one, let's delete it. 3:39
    All right, there's one more thing we should change here. 3:44
    Can you guess what it is? 3:47
    One of the properties of our fact book is all of the facts it contains. 3:48
    So this facts array should really be a property, field or 3:52
    member variable of our fact book and not a local variable of the getFact method. 3:55
    Let's cut the facts declaration from the getFact method, And then paste it up here. 4:00
    Next we're going to test the app. 4:15
    But first, just for fun, I'm going to show you another way we could have done this. 4:17
    You don't have to follow along with this part, but you're more than welcome to. 4:22
    I'm going to use Cmd or Ctrl+Z to undo all the way back to here. 4:26
    Then I'll right-click on the facts variable, and select refactor. 4:30
    But instead of picking rename I'm going to choose extract, and then field. 4:39
    Then I'll choose where to initialize this new field, I'll pick field declaration, 4:46
    which will put it at the top of the class, and then hit enter. 4:52
    And then we go, 4:58
    Android studio automatically factored our local variable to a field. 5:00
    It even deduced that our facts variable can be declared as final 5:04
    because we never make any changes to it. 5:08
    Its functionality equivalent to what we had before. 5:10
    But just to make it look exactly the same I'll delete the final keyword and 5:13
    this optional new string bit. 5:17
    And finally I'll cut and paste our comment to be above our new field. 5:26
    There are tons of helpful tricks like this in Android Studio. 5:35
    And they get even faster when you start using the keyboard shortcuts. 5:38
    Last but not least, we're getting a couple of warnings from Android Studio. 5:42
    Each of them is just letting us know that we can use a stricter access modifier. 5:47
    And luckily, we can fix both of these just by using Alt+Enter. 5:51
    But enough about that, we'll have more time for tips and 6:02
    tricks once we get the basics down. 6:04
    For now, let's run our app to test it. 6:07
    Remember, the goal of refactoring is to make changes to the code 6:13
    without changing the behavior of the app. 6:16
    So it should work exactly the same as before. 6:19
    Great work. 6:27

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