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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!

Things to Consider

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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