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We left our code in
a pretty fragile state.

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We could definitely add way too
many Pez to our dispenser and

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have a big mess on our hands.

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Now, luckily, Java provides a way for

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us to let the user of our objects know
when they've done something wrong.

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I'm talking about exceptions.

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It's possible for us to tell the consumer
that we are having problems with how

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they're using our object.

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Now, stated another way,

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we can let them know that
an exceptional event has occurred.

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And it's possible for the user to be
able to handle or catch that exception.

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The way we do this on the usage
side of things is what is known as

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a try/catch block.

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Now, unlike what this little guy here
might tell you, there actually is a try.

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Let's go use it.

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So Java comes with some built-in
exceptions and you can create your own.

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Now, we'll cover creating custom
exceptions in a future course.

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But for now, I'd like you just to
get familiar with how they work.

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So since we're dealing with
a case where an argument that

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was passed into our method will
actually break the object.

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One exception that we could use is one
that's known as the illegal argument

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exception.

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So let's use it.
All right, so to do it,

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let's rework this code a little bit here.

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So instead of just letting the fill
happen, let's go ahead and

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we'll store a new variable
called newAmount.

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And we'll store the current pezCount
plus the pezAmount that was passed in.

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Okay, now, if this new amount
is more than we can store, so

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if this new amount is more
than we can store, right?

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We know that there's a MAX_PEZ limit.

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So if it's bigger than that, then we need
to let them know by throwing an exception.

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Now, most exceptions take a message.

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So what this looks like is you say throw,
and we're gonna make a new,

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sorry, throw, we're gonna make
a new IllegalArgument, and

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spelling matters here, Exception,
IllegalArgumentException.

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And most of them take a message,
which we will push here, and

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we'll say, Too many PEZ!!!!

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So what will happen is this will be
thrown and we'll exit the method.

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So the code will have
exited before it gets here.

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So we can safely go ahead and
do this, right?

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We know that this is safe.

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So again,
we see what it would possibly be.

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If it's more than what's allowed there,
we throw this exception.

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So let's go see what happens, what it
looks like when an exception happens.

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So let's save this.

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And again, we're talking about the illegal
argument of this pezAmount is illegal.

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Okay, so over here, let's go ahead and
let's say after our last

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little loop here of testing things,
let's say dispenser.fill and

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let's put a crazy number there,
let's fill with 400.

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And what I wanna show off
is that at the bottom here,

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because that exception happens,
that exception is going

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to do what is known as bubbling,
it's gonna bubble up here.

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This will never happen.

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This line is never going to happen
because the exception is going

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to be thrown here as well.

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Okay, so let's go ahead and
run this and see.

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So we'll say clear && javac

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Example.java && java Example.

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All right, so
we should see a pretty nasty stack trace.

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So exception in thread main, Too many PEZ.

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So we tried to fill it in and
it blew up, and

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see here it's showing where it happened.

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This is our stack trace that
happened in PezDispenser on line 18.

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That's where we threw the exception at,
cool.

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So instead of getting this
ugly error message back and

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exiting the program hard like we did,
right?

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Because this line, this will never happen,
didn't happen, the program just exited.

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Just like the other method,
it just exited.

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We can actually wrap this
in a try catch block, and

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this will let us handle the exception and
continue.

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Here, let me show you.

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So we'll say try, and
we're going to open up some new scope and

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I'm going to close some
new scope right away.

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And let's go ahead and I want to move both
of these lines inside of that try scope,

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that try block there.

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Okay, and so what happens is it comes in
here into this and it will try it and

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if not, it will catch anything and
you can be very specific here.

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So we're going to say specifically I only
want to catch IIllegalArgumentExceptions.

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Now typically I name each one
of these what they are there.

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So iae, IllegalArgumentException.

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So totally a style thing.

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And what we can do is this code will run.

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If something fails in here, specifically
if an illegal argument happens,

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it will run this code here.

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So let's say,
we'll say System.out.printline Whoa there!

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And we will, let's just show that
you can get the message, right?

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That catch there is
gonna pass in that iae,

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The error was %s.

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So what we can do is we
can say iae.getMessage and

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that will get the message that we passed
into the constructor of that, right?

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So remember we passed in this message,
Too many PEZ, so

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we pass that in there, Too many PEZ.

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All right, so let's run that again.

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Cool, as well there,
the error was, Too many PEZ,

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I forgot to put a new line there.

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But what's cool is it didn't print this,
this will never happen, right?

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Because it can't,
it's not going to get past this, and

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it's going to run this
line here this code.

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Awesome, so we've successfully blocked our
Pez dispenser from getting over filled.

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Great, now we have a way of communicating
when our object is being used incorrectly.

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Throwing and catching exceptions
is very common in Java, so

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it's good to get yourself
familiarized with them.

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Some newcomers to Java will often complain
about how many exceptions are used and

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defined.

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But it's part of what leads
to Java's famous stability.

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You can actually define that
a method might throw in exceptions.

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And then anyone who uses that method will
need to either protect against it or

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throw it themselves.

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We'll touch on these in
upcoming courses and

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you'll encounter them in
the standard Java libraries.

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If you'd like to see more information
on this, check out the teachers notes.

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The exception type that we just used
IllegalArgumentException is called

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a runtime exception, and therefore,

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we don't need to declare
it at the method level.

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By anticipating how things might go wrong,
we can provide a stable,

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testable object that can easily
integrate into existing products.

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So, now that we can fill, and dispense our
Pez dispenser, as well as know that if

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people misuse it, will warn them,
I think we are done with our first object.

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If what I warned you about comes true,
and you do indeed start imagining how

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everything you see in real life
could be implemented as an object,

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please head to the forum, use it
much like you would a support group.

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We're all going through the same thing,

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and a little comradery can really help
in situations like this, it gets better.

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Make sure to check the teacher's notes and
extra credit section if you're looking for

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more practice.

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Also, thanks again for
your feedback and ideas.

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It really is helping us to ensure that
we are building the best courses with

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the skills you need and want.

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Please do hang out in the community
forums, ask questions, answer questions.

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And remember this little tidbit of
wisdom from this guy's dying breath,

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pass on what you have learned.

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Thank you so much for hanging out and
I hope you had as much fun as I did.

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Looking forward to seeing you very soon.

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See you at the next course,
right after this exercise.