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[MUSIC]

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Now that we're comfortable using
the design editor to make changes to our

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layouts, it's time to write some code.

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Let's start by taking a look
at some of the code that was

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automatically generated for our project.

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Using the Android perspective
makes our code easy to find.

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It's right here in the Java folder.

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But if you happen to be in
the project perspective,

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remember that our Java code can be found
at app > source > main and then java.

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It's right above our resources folder.

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Let's switch back to
the Android perspective.

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And then let's look
inside the java folder.

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Now we can see the package name we
choose when we create our project.

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This is where all of
the code will go by default.

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Inside this package we find
one file FunFactActivity.java.

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It's not showing the .java but it's there.

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And if we double click on it,
it opens over here in the editor.

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Now we can close the rest of these files.

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Let's right click on FunFactsActivity.java
up here and choose Close Others.

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And we'll go ahead and
hide the project view for now.

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In Android, an activity represents
a screen that users can interact with.

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We'll learn much more
about activities later.

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But for now,
let's focus on this onCreate method.

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The onCreate method is called when
our activity is first created and

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since our app only has this one
activity this onCreate method

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will be called when our
app is first started.

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You might have noticed that this
method also has one parameter,

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a bundle names savedInstanceStae.

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We won't be using this variable in
our app, so let's ignore it for now.

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Inside onCreate, the most important
line is the call to setContentView.

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This method tells the activity which
layout file to use for the screen.

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This R.layout.activity_fun_facts
parameter is an id which points

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to the activity_fun_facts XML
file in the layout directory.

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This is where the layout we've been
working on gets attached to our activity.

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Okay, time to make the magic happen.

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The first thing we need to do is
declare two fields or member variables.

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One for our fun fact text view and
one for our button.

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A field is the name for

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a variable that is inside the class but
outside all of the methods.

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Using fields for

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our views means that we'll be able to
access them from any method in our class.

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This is especially useful because
there is often more than one method

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that needs access to our views.

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Let's start by adding a line
at the top of the class.

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Then let's add a comment to
help explain what we're doing.

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Remember, it's two forward slashes for
a single line comment.

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Let's type // space, and then,
say, declare our view variables.

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Then on new line,
let's declare our fun fact

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text view as private
TextView FactTextView.

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And if TextView is in red,
that means we haven't imported it yet.

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So put your cursor on it and
hit Alt + Enter to import it.

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Also, note that we won't be using
the m prefix for our fields.

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According to the Android
source style guide,

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all fields should start with
a lower case m, like this.

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However, most code isn't written that way.

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So unless you plan on contributing
to Android's source code,

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feel free to drop the m prefix
as we'll be doing here.

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If you'd like to read more
about these style guidelines,

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check out the link in
the teacher's notes below.

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Now we need to declare our button.

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Let's add a new line
below our text view and

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type private and then start typing Button.

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Notice that Android Studio is
trying to guess what we're typing.

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Once the top choice is Button,
hit Enter or

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Tab to let Android Studio
autocomplete that for us.

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It even adds the import statement.

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Then, when we type a lowercase b,
Android Studio suggests a name of Button.

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Cool, right?

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But we'd rather have
a more descriptive name.

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Let's name it showFactButton.

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All right, but why did these
names change to grey like this?

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If we hover over one of our fields,

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we get a quick tip saying
private field is never used.

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The grey coloring will go away
once we use these variables.

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Another thing I want to point
out are the import statements.

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We can view them hitting
the little plus button up here.

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By default,
our class only has a couple of imports.

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But every time we use the new class,
like TextView or Button,

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Android Studio will try to automatically
add the corresponding import statement.

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If you use a class that isn't yet
imported,

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let's say I delete the Button import.

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Then you'll have something
that looks like this.

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To fix it, just place your
cursor on the missing class and

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hit Alt + Enter to import it.

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Let's take a short break and

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then we'll see how to assign our
views to these new variables.