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You have completed Java Arrays (2017)!
You have completed Java Arrays (2017)!
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Let's explore two dimensional arrays. An array of arrays. Rows and Columns.
Copy and Paste
// Ben's
{1, 2, 4, 2, 6, 5, 4, 3, 3, 2, 5, 7, 2, 7, 8, 4, 3, 2}
// Alena's
{2, 3, 5, 1, 1, 2, 3, 1, 1, 2, 4, 1, 3, 3, 2, 6, 3, 2}
// Pasan's
{4, 4, 2, 1, 2, 2, 1, 4, 2, 2, 2, 3, 2, 5, 8, 1, 2, 2}
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Let's talk about multi-dimensional arrays.
0:00
They sound kinda out there, don't they?
0:04
Like science-fictiony or time-travely.
0:06
Well, don't let the name make it
more difficult than it needs to be.
0:08
We're going to explore
two-dimensional arrays,
0:12
or 2D arrays,
which is really just an array of arrays.
0:15
Now the arrays that we've been working
with have been one-dimensional.
0:20
Now 2D arrays are super handy at helping
to describe things in rows and columns.
0:23
If you've used a spreadsheet before, you
can definitely imagine this sort of thing.
0:29
In fact, why don't we just start there?
0:33
So here I've created some golf
score cards using a Google sheet.
0:35
And you can see that I have three score
cards here for each of my friends, Ben,
0:39
Alena, and Pasan.
0:43
They were the same ones at the movies,
we do everything together.
0:44
So these are rows, right?
0:47
Each one of these is a row,
and this is a column, right?
0:50
So this is a column.
0:54
And if I wanna talk about a specific one
of those cells, I can reference it, right?
0:55
So this one here, you can see is B2, and
1:00
this one here is B3, and C3, right?
1:04
Now as we saw with our Ben score card
array, we were able to represent this row,
1:08
Ben's row here, we were able
to represent this as an array.
1:14
But what we're getting at is that
we wanna have these other two cards
1:20
in the same array.
1:24
So now what we wanna do is we wanna
make a new array that has all of this,
1:25
it's gonna have all of these,
each entry is an array.
1:30
So, let's turn this
spreadsheet into an array.
1:36
In the teacher's notes, I've pasted
each of these rows as an array literal.
1:40
I wanna show you how to create this and
then I want to explore it a bit.
1:45
So, first let get it into JShell so
we can play with it.
1:48
But I don't know about you,
but I make mistakes.
1:53
So, one nice trick when making multiple
line statement in JShell just to create
1:57
a temporary file and
then have JShell read it.
2:02
Here, let me show you.
2:04
So, in our workspace,
I am gonna create a new file, and
2:06
I'm just gonna call it scratch.java.
2:10
And we'll use this as
the scratch pad of sorts,
2:13
right, whenever we want
to import things here.
2:16
So, let's define our array.
2:19
You just declare a normal integer array
and remember we want an array of those.
2:21
So you just make one more.
2:28
And then we'll name it scoreCards,
so scoreCards.
2:31
And then we create our
first array literal.
2:38
So we'll say that, and
this is an array, and
2:42
now our array is going to
contain arrays of integers.
2:45
So, let's copy and past Ben's score
card from the teacher's notes.
2:49
So I'm gonna do that and paste Ben's note,
and I'm gonna add a comma,
2:54
cuz that's the first row, and
then I'm gonna add Alena's.
3:00
And I'm gonna add a comma.
3:10
And then I'm going to add Pasan's.
3:11
And now if we bring our spreadsheet
over here and we look at it,
3:18
we have just the same thing.
3:22
So we have 1, 2, 4, 2 for Ben,
1, 2, 4, 2 then for Alena,
3:25
we have 2, 3, 5, 1 and we have 2, 3, 5, 1.
3:29
Cool, and Pasan's 4, 4, 2,
1, 4, 4, 2, 1, awesome.
3:33
So now let's get this
imported in the JShell.
3:37
So we have a file here,
it's called scratch server, saved it,
3:41
also I'm gonna go ahead, I wanna put
a semicolon there as a good citizen.
3:45
And I'm gonna run jshell.
3:49
Bring this up a bit here.
3:54
I'm gonna say /open scratch.java.
3:56
And what that does is it runs
this file and it's now available.
4:04
So now I have a variable
called scoreCards.
4:07
And you'll see that here it is,
it's a multidimensional array,
4:12
the first one is 3 cuz there's three rows
and each one of the rows has 18 columns.
4:18
And remember it really just is
an array of arrays, right, so
4:27
if I look at scoreCards.length, We'll see
that it's 3, that's the number of rows.
4:31
So, to get the first row we just use
index 0, cuz array is a zero based.
4:40
So we'll say score, I'll Ctrl+L here, and
4:46
we'll say scoreCards[0], and there we go.
4:50
It's the first row.
4:55
So this was Ben's score that we pasted,
right?
4:57
So this is Ben's, this is the first one.
5:00
This was Ben, and
the second one here is Alena.
5:01
So let's see how she
did on the fourth hole.
5:07
So that would be
scoreCards[1] to get Alena.
5:11
And then we wanna get the fourth hole,
which again,
5:17
because we're zero-based here too,
would be the third index, right?
5:19
So we'd say [3].
5:24
So right cuz it's for
zero, one, two, three.
5:25
So we get,
awesome a hole in one nice job Alena.
5:32
So now you do that.
5:36
Let's see, I want you to do this as
show me what Pasan got on the 15th hole.
5:39
Remember this is Pasan here.
5:48
So go ahead and access that, and
just print it out here in JShell.
5:50
Go ahead, pause me.
5:53
Did you get it?
5:56
So Pasan happens to be
5:57
The third row which is index 2 and I want
the 15th hole, so I need to subtract 1
6:03
from that to get 14 because both
of those are zero-based, right?
6:08
8, come on buddy, keep practicing man,
you'll get better at this golfing,
6:14
don't worry Pasan.
6:18
I know, let's do this.
6:19
Since we have two arrays, the friends
array and the scoreCards array,
6:21
why don't we loop and
print out all their scores?
6:25
Why don't we take a quick break and
let this sink in a bit.
6:30
Now, taking breaks is a super important
habit to get into for learning.
6:33
So, why don't you take a stretch and
get some fresh air.
6:37
While you're out, let your brain
wonder about 2D arrays a bit.
6:40
Think about how they're just like
the spreadsheet here, right?
6:44
They're just like the spreadsheet
with rows and columns.
6:48
And think about how you can access
them much like, like here is P4,
6:51
this 8 was the same that was row 2,
14, right?
6:56
For it to get to Pasan, 2, 14.
7:01
It's very similar, right?
7:03
One thing that I wanna point out before I
let you go here, you can also add another
7:05
dimension to get a 3D array, but
you have to wear glasses to see it.
7:09
Just kidding.
7:14
But seriously, you can keep appending
them out as far as you'd like, but
7:15
it gets weird quick.
7:18
So when you come back,
we'll loop over our score card.
7:20
Sound good?
7:23
See you in a bit.
7:24
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