- Constants 7:23
- Add a Constant 1 objective
- Filling the Dispenser 7:17
- Changing State 2 objectives
- Abstraction at Play 8:34
- Computed Properties 2 objectives
- Incrementing and Decrementing 8:28
- Increment and Decrement 3 objectives
- Method Overloading 8:00
- Overload Methods 2 objectives
- Exceptions 7:50
- Throwing Exceptions 1 objective
- Handling Exceptions 1 objective
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Incrementing and Decrementing
8:28Learn some math shortcuts that integers provide
We are finally to the point
of writing our objects,
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arguably most important method ever,
dispense.
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Like I was saying earlier,
if we wanted to go overboard,
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we could actually make
one of these Pez objects.
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Nothing's stopping us, right?
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You could totally imagine it.
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Our new Pez class would define some state,
like flavor.
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Maybe it could even store the time that
it was inserted into the dispenser.
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We could determine if it was stale.
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When we call the dispense
method we're about to write,
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we could actually return
one of these Pez objects.
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Or that's going a little overboard,
let's not do that just yet.
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Now, I was being a little silly there.
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But this is actually a pretty hard thing
that you're going to grapple with.
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How do you know when to
stop building objects,
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because like we talked about before,
everything can be modeled as an object.
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I struggle with this all the time.
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A common acronym that you'll probably
start hearing a lot is YAGNI.
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You ain't gonna need it.
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In fact, I keep a sticky on my laptop and
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it helps me to remember not to
overengineer before you actually need it.
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Now there's another one that's
pretty common sense, but boy,
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do we forget it the more
we start programming.
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And that's this, KISS.
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Keep it simple, smarty pants or
something more rude than that.
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So, with that said, let's keep it simple
and assume that there is only one flavor.
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What we'll do is, as long as there is a
Pez to be dispensed, we will return true.
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Of course, if it is in fact empty,
we'll return false.
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Sound good?
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Let's do this.
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Okay, so I have JShell open again and
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I wanna show off a couple of cool
tricks that we can do with integers.
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Okay, so first off we know
that we can create one, right?
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So we're gonna say, int example = 1.
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And if we wanted to just add one to it,
we could use the variable itself.
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So we can say something like,
example = example + 1, right?
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So that's gonna return 2.
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So, we've set, now example is 2, right?
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So, since that's so common,
there is a special shorthand for it, and
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it looks like this.
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So you say example += 1 and
basically it's this.
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It does exactly this,
it's just shorthand for it.
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Cool, so that, return 3 and
also updated example to be 3.
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Okay, finally,
because we end up adding one a lot,
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there's an even shorter form and
it's called incrementing.
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And it looks like this.
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So we say example++.
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Now this one's a little bit dangerous.
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It actually returns first and
then changes the value.
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Because this is what is
known as post incrementing.
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So if we do this, it's gonna go ahead and
it's stored 3 in 5.
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Now remember, example was 3.
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But if I look at example now, it's 4.
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So it actually did example plus one.
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But it returned, the expression itself
returned what the value used to be,
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much like that swap head that
we were looking at earlier.
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But you can actually do the other
side too, you can do pre increment.
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So you can say example, ++example.
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And that returns 5 and example is 5.
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And that does the reverse, right?
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It increments and
then it returns the value.
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Now the dangerous thing about this
is that you can use these in a very
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complex statement.
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Now if you can't do the incrementing
on a line by itself,
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I highly suggest you
don't use these at all.
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In other words, I highly recommend that
you don't use the value returned from
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either the pre or post increment.
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As you can probably guess by now,
the same works with subtracting.
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So I'm gonna clear here and
we have, example's 5 so
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we say example = example- 1.
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We'll see that that example is 4 now, and
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you can also do example -=1 and
example's now 3.
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And then, finally, as the other one is
called incrementing, with the pluses,
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this is called decrementing.
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So we can say example-- and
we did it on the other side, so
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it's post but now example's actually 2.
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Well, decrementing sounds like
exactly what we need to do
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when we want to dispense.
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Again, so the dispense method that we're
gonna write should work like this.
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Every time that we dispense,
we should decrement the Pez count,
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as long as there's some left.
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And we should let the caller know
that we dispensed something, cool.
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So, in PezDispenser,
let's move this down here.
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Let's go ahead and
we'll make a new method.
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It's going to return a true or
false, right?
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And it will have it be called dispense,
and it won't take anything.
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So, we'll store the default value here,
we'll say boolean
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wasDispensed, and
we'll set the default value to false.
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Okay, so we know that we can
say if it's not empty, right?
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So, let's look at this code block.
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So if it's not empty we want
to decrement the Pez count.
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So we do that as such,
we say pezCount--, so
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that whatever is in there moves down one.
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And we're gonna say wasDispensed,
we're gonna set that equal to true,
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because it was actually.
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And then finally,
we're going to return what was dispensed.
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So it will start out as false, if there's
anything in there it will go through.
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If it's not it will never come in here and
it will just say false and
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the number won't go down.
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Makes sense?
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Okay, so
let's flip over to our Example.java.
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And I'm going to drop out of
the JShell here if we do Ctrl+B.
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And I will say clear, all right.
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So in Example.java here,
let's just go ahead and
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empty the whole thing in one sitting.
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We're probably all guilty of, I know I am.
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So, this should be fairly easy.
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All we need to do is just call
the dispense method 12 times, right?
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Well, that worked, but
this sounds like a job for a loop.
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We want to keep dispensing as
long as we get something back.
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So, while there's something dispensed,
eat it.
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Sound good?
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Sounds like a while loop right?
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So, just a quick reminder, so
we'll say while dispenser.dispense().
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Well that's happening,
let's just write out chomp I guess, right?
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And then finally, if it is actually empty,
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which it should be,
cuz we're gonna eat them all.
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We'll say system.out.println(Ate
all the PEZ).
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Something's not lining up,
look, I forgot a quote here.
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There we go.
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All right, so
this is gonna return true or false.
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And as long as it's returning true,
it's gonna keep on chomping.
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Sound good, let's take a look.
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Clear && javac Example.java
&& java Example.
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Here we go, chomp, chomp,
chomp, chomp, chomp.
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We ate all the Pez, cool.
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So we should have 12 there, chomp, chomp,
chomp, chomp, chomp, chomp, chomp,
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chomp, chomp.
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Ate all the Pez, awesome.
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Good job, we can now load and
dispense our Pez.
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We are getting close to
completing this model.
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Now that we're removing Pez, we should
probably get more specific around
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the handling of what it means to fill.
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In the real world,
if we try to load a dispenser that
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already has some Pez in there,
we'd add Pez until it was is in fact full.
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We wouldn't just add the maximum amount
available, because that could be
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potentially overfilling and wasting
the remainder, we don't wanna waste.
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Let's practice incrementing and
decrementing.
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