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Access Level Modifiers
3:55Access level modifiers such as public and private help to explain our intent.
All right, so we left a little
problem in our PezDispenser class that
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I want to go in and fix with you.
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We made a field that exposes
the character's name, and not
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only can we access the field to get the
current value, but we can also change it.
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Now in real life, we can't really
change the character of a PezDispenser
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after it's been created, can we?
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Yet, as we saw,
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you can do exactly that with the newly
created object we just made.
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We never want people to misuse the object
that we allowed them to create.
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But it's kind of only us to blame, right?
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We allowed that to happen.
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We should make it as clear as
possible to consumers of our class,
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how we intend them to use it.
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Now when I say consumers,
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I mean the developers who
are going to be using your code.
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This might seem like a strange concept,
but
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it's one that I think is super
important to grasp early on.
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Are you ready?
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Other people are going to use your code,
they are.
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They need to be able to look at your work
when you aren't there to explain it, and
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they will need to be able to understand
how you were intending it to work.
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And of course,
sometimes that person is you.
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Sometimes you forget what
you were trying to convey.
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It always behooves you
to be more explicit, and
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Java is very good at letting
you express yourself.
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It's part of this verbosity that makes
things challenging in the beginning but
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shines bright once you grasp the concepts.
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So in order to communicate how you
intend people to use your objects,
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you can add some additional
qualifications to your statements.
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In Java these are referred to
as access level modifiers.
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There are keywords that you can
add your field definition to
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further specify who is intended
to access the information.
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A table similar to this is
found in the Java SE tutorial,
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I've linked to in the teacher's notes.
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So our current field isn't using
any of these modifiers, public,
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protected or private.
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So it falls under this row
here that says no modifier.
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Now we haven't gotten to packages just yet
but you can think of that for now as
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files in the same folder or directory,
which is exactly what we're seeing.
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In fact, why don't we remove
what we haven't covered yet?
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Now our code in the example file
was able to access the field,
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because it's in the same folder or
package as the PezDispenser class.
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So let's fix that.
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In order to ensure that code in the same
folder cannot access our field,
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which of these should we use?
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That's right,
we should mark our field as private.
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Let's do it.
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Okay, so it's pretty straightforward to
mark a field as private, all you need to
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do is put the access level modifier
before the type declaration, right?
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So it's String type declaration here,
so I wanna put private and that's it.
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Now let's try and rerun our code,
and remember here's our code here.
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So, we're gonna say a clear and
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javac Example.java and java Example.
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And bam, our code doesn't even compile.
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Do you see how explicit that is?
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The code doesn't even
work if you misuse it.
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Now that's pretty powerful, right?
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So here what this first error is saying,
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is it's saying it has private access
in the PezDispenser so it can't set it.
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But, wait a second,
there's a second error here.
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It's not even accessing the value at all.
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We can't even get the value.
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[LAUGH] That's some pretty
good protection, right?
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So we've completely hidden the part of
our state to anything at all except for
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the class itself over here.
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This is the only bit
where this is accessible.
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Nobody else knows about this,
not even instances of that class.
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Now this kind of hiding is used for
very deliberate purposes.
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This is called encapsulation and
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will delve deeper into this
concept as the course progresses.
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But for now,
how do I get access to that value?
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I'd love to be able to at least
show the current character.
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Well, the most common way
to expose a value but
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not let someone set it
is by adding a method.
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So we best learn how to add methods.
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Let's do that next.
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