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You have completed Java Objects!
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You can protect your variables from re-assignment using the final keyword
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Okay, so over the past few lessons,
0:00
we have successfully picked up
some language constructs to
0:02
explain that a character name is
required to create a new Pez dispenser.
0:06
And after it's been created,
you currently can't change that character,
0:10
which was exactly what we
were intending to convey.
0:14
Because we're modeling
what happens in real life.
0:17
Getting so
close like we just talked about though.
0:20
What if someone on our team doesn't
know that these heads can't be changed.
0:23
And they come in and write a new method
that does just that, it changes the head.
0:28
No, we'd hopefully,
catch that in a review of their code, but
0:32
we can do better than that.
0:35
Let's simulate the scenario and
0:37
I'll introduce a concept that
will help solve the problem.
0:39
So let's go ahead and
assume that a developer on our team,
0:42
let's call him Chris.
0:45
He grabbed our Pez dispenser class and
decided to make a new method
0:47
that would change the character head and
return the previous one.
0:50
So let's walk through that
method creation really quick.
0:54
Let's see, obviously,
Chris made that public, right?
0:57
He wanted somebody to use
it because it's useful.
1:00
And like we said, it's gonna return the
original character as the return value.
1:02
So that's a string, and
then we'll name it.
1:06
Let's call it swapHead cuz
it's gonna swap the heads up.
1:09
And it's callable so,
we're gonna open parenthesis.
1:13
And it will declare a parameter of type
string that represents a character name,
1:15
right?
1:21
So we're gonna ask that somebody
passes in the new character name.
1:22
And then we're gonna open up the method
body, and I'm gonna close it right away.
1:25
Uh-oh, we've got that naming
collision problem again, right?
1:29
So look, here's a character name.
1:32
And we wanna swap out the character name,
so
1:33
we know how to deal with that though,
right?
1:35
So first, what we wanna do is get
a hold of the original character name,
1:37
so that we can store it in a variable.
1:41
So let's be clear about it.
1:43
Let's say, string originalCharacterName.
1:45
And we want to make sure that
we keep this character name.
1:51
So we're gonna say, this.charactername,
not running into that naming collision.
1:55
We're not gonna fall for it, right?
1:59
Cuz this is in scope.
2:01
And now, what we'll do is we'll swap out
this characterName with the characterName.
2:03
So basically, all we're doing
is just keeping a safe copy
2:10
of what was originally in there because
that's what we wanna return, right?
2:14
So we're gonna return the original,
2:17
[LAUGH] I keep on typing
the originalCharacterName.
2:20
So now, if we walked over to this method,
but we didn't want Krista, right?
2:27
We can show you how it's used.
2:34
So we're gonna say,
2:36
before = dispenser.swapHead.
2:39
And we're gonna put in bring back
the Darth Lord again, Darth Vader.
2:44
And we're gonna print
2:50
out ("It was %s but
2:55
Chris switched it to %s.
3:00
And then we'll do a new one.
3:07
And so we want to first,
let's first %s as before, right?
3:10
So before,
it was what came out of the dispenser.
3:15
And then next, we're gonna say, dispenser.
3:18
And we're gonna call our own
method getCharacterName, cool.
3:20
And we end that line.
3:25
All right, so I'm gonna save it.
3:27
And then I am going to say,
3:30
clear && javac Example.java
&& java Example.
3:32
What do you think, is it gonna work?
3:38
I think so, I think you did it.
3:40
Yep, so there it is.
3:44
It was yield up at Chris
switched to Darth Vader.
3:45
Chris did exactly what we
didn't want him to do.
3:47
He changed the head.
3:49
Come on, Chris.
3:51
But we can't really buy him, can we?
3:52
We didn't make it very clear.
3:54
We could have at least left a comment so
he knew.
3:57
Then actually, there's something
way better than a comment.
3:59
Something that would stop Chris and
his tracks, even better.
4:02
It wouldn't even let him compile and
that's the final keyword.
4:05
So when you want a variable to
be assigned once and only once,
4:09
you market with the final key word, final.
4:14
So now, if we go and we try to run this
code, we'll see that Chris got blocked.
4:20
You cannot assign a value to
the final variable characterName, and
4:25
that is happening from inside line 14,
right?
4:30
So the PezDispenser line 14 if
we come in here to line 14.
4:33
Sorry, in the PezDispenser
class [INAUDIBLE] line 14,
4:38
that's in the swapHead, okay?
4:41
Cuz we assigned it once here.
4:43
And he's trying to swap it here,
it's telling that.
4:45
In a more advanced editor which
we get to hear in a few courses.
4:48
This would have warned him very loudly
before he even tried to compile.
4:51
So again, final here, says that this
variable characterName is declared,
4:54
it can only be initialized once,
it doesn't allow for any more assignments.
5:00
Now, you can use the final keyword for
more than just field.
5:07
You can use methods in even classes.
5:09
Check the teacher's notes for more.
5:11
I'm gonna go ahead and say, sorry Chris,
you can't do this, you're out of here.
5:13
Let's give her this.
5:17
And I'm gonna get rid of this line over
here, because now, we have protected it.
5:18
And that code makes no sense, awesome.
5:24
This video is the final one in this stage.
5:27
And I know, I know,
you're probably like, finally!
5:30
You're doing great.
5:33
And don't worry, I've been
intentionally taking things slow and
5:34
making sure that you can read the intent
of Java code when you come across it.
5:37
Also, now, you can write it.
5:41
Now, that we got the basics in place.
5:42
We've got fields,
access modifiers, methods, and
5:45
constructors, let's
pick up the pace a bit.
5:47
I think it's finally time for
5:50
us to start working through the core
features of this Pez dispenser.
5:51
I know our little dispenser object
isn't very impressive at the moment.
5:54
Let's do something to change that.
5:58
Let's wrap up this stage so that we can
get some Pez in and out of this thing.
6:00
But first, let's do a quick practice
review of what we just learned.
6:04
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