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It's often helpful to group items together into an array. In this video, we'll create an array of facts. Then we'll use our randomNumber to help us pick a random fact!
Facts (for copy/paste):
String[] facts = {
"Ants stretch when they wake up in the morning.",
"Ostriches can run faster than horses.",
"Olympic gold medals are actually made mostly of silver.",
"You are born with 300 bones; by the time you are an adult you will have 206.",
"It takes about 8 minutes for light from the Sun to reach Earth.",
"Some bamboo plants can grow almost a meter in just one day.",
"The state of Florida is bigger than England.",
"Some penguins can leap 2-3 meters out of the water.",
"On average, it takes 66 days to form a new habit.",
"Mammoths still walked the earth when the Great Pyramid was being built." };
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We just programmed the heart of our app,
the random number generator.
0:00
Now we need to use that generator
to help us pick a random fact
0:04
on each button click.
0:08
But before we can do that,
we'll need a pool of facts to choose from.
0:09
Let's start by creating
an array to hold our facts.
0:14
Remember, an array is just a container
that holds values of a specific type.
0:17
Let's add two lines to the top
of the onClick method.
0:22
And then type String, facts.
0:27
We now have a new variable called facts,
and
0:33
we've declared it to be an array
of strings, or a string array.
0:35
You can make an array out
of any type of object.
0:40
All you need to do is add square
brackets after the data tag.
0:43
All right, now for
the assignment side of things.
0:47
For the sake of time,
I'm going to paste in the ten facts and
0:50
then we'll go over the syntax.
0:54
You can type these out if you want, but
I've put this code in the teacher's notes
0:56
so you can just copy and
paste as well, let's do it.
0:59
I'll select everything after
the word facts, up to but
1:03
not including the semicolon.
1:07
Then I'll copy this and
paste it between facts and
1:09
the semicolon back in the onClick method.
1:13
And now we can see that one
way to initialize an array
1:16
is with an comma-delimited list
between two curly brackets.
1:19
Now that we have an array
of strings to select from,
1:24
let's use our random number generator
to help us pick one at random.
1:27
Our array has ten elements in it.
1:31
Let's start by changing our
random number generator
1:33
to have a range of 10 instead of 3.
1:36
If we clicked on our button now, we'd
see random numbers ranging from 0 to 9.
1:41
And what else do we have
that ranges from 0 to 9?
1:47
That's right,
the indices of our facts array.
1:49
This first fact about ants is at index 0.
1:52
And this last fact about
mammoths is at index 9.
1:56
So if we want to select a random fact,
we just need to select the fact
2:00
from our facts array that's at the index
of the random number we generated.
2:04
It seems easy enough.
2:09
Let's start by getting rid of what we're
currently setting our fact to, And
2:11
then type facts,
in square brackets, randomNumber,
2:18
to select the fact at
the index of our randomNumber.
2:23
All right, that should do it.
2:29
But before we test our app, there's
a potential bug we should fix first.
2:31
What happens if we add a new
fun fact to the array?
2:35
Can you tell where the code will break?
2:39
I'll add another fact and
then let's talk about it.
2:41
I'll say,
2:43
Treehouse is not actually in a tree.
2:49
Now that we have 11 elements in our array,
2:55
we need to change 10 to 11 down
here in our call to nextInt.
2:58
But if we forget to change it, we'll
never see our new fun fact in the app.
3:02
Wouldn't it be nice if we could somehow
use the number of elements in the array
3:07
as our parameter instead of
a hard-coded number like this?
3:11
Then we wouldn't have to change
it every time that we add or
3:14
remove elements in our array.
3:17
Sure enough, Java has a way for
us to do this.
3:19
Let's delete the number 10 here and
type facts.length.
3:22
This gives us the length
of the facts array,
3:28
which is another way to say
the total number of elements.
3:30
By using this property of the array,
3:33
we will always pass in
the right number of elements.
3:36
This saves us the work of having
to manually change numbers and
3:39
it also protects us from errors.
3:42
For example, if we had deleted an element,
I'll delete this one that I just added,
3:45
But we left this number as 11, then our
app may try to reference an element that
3:54
doesn't exist and it would crash.
3:58
Looks good to me, let's click on
the run button to test our app.
4:01
And then we can tap the button and
we should see some of the new facts.
4:07
And there we go,
4:12
mammoths still walked the earth when
the Great Pyramid was being built.
4:13
And if we keep clicking,
we should eventually see all of our facts,
4:18
very cool.
4:23
Awesome work, don't worry if all these
new Android words aren't sticking yet.
4:26
We've done a lot and
we still have a lot to do.
4:31
But if you stick with it,
I'll explain everything you need to know.
4:34
And if you want to talk about
anything you're stuck on,
4:37
head over to the community for
questions or discussions.
4:40
It's easy to feel
overwhelmed with this stuff.
4:43
But trust me, things will start to
make more sense the more you practice.
4:45
On that note,
why don't you try some more practice?
4:50
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