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[MUSIC]

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Hello, and welcome back.

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I'm Craig and I'm a developer.

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This course is going to build on top of
what we learned together in Java basics.

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If you haven't checked it out yet,

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I recommend that you follow
the link in the teacher's notes.

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It's a prerequisite for this course, but

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you don't need to have any
other programming experience.

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And what we're going to learn in this
course is relevant to many other

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programming languages that
you're going to encounter.

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Don't forget that there are speed
controls on the video player.

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Feel free to speed me up or
slow me down to your heart's contempt,

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I won't mind at all.

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In this course,
we're going to be talking about objects.

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Java is an object oriented
programming language,

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and literally everything
in Java is an object.

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Well, except for the primitive
types like int and Boolean, but

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even those have wrapper
types which are objects.

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So as you can imagine, understanding
objects is super critical to your

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foundational base of the Java language.

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And I'm excited to explore them with you.

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So first we'll familiarize ourselves
with the basics of objects.

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How to use them, how to create them,
and then after we get a good grasp,

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we'll build an application using them.

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Along the way we'll be expanding
our Java toolset, again,

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learning new tricks as we need them.

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Just like we talked about in Java basics,
there are gonna be a lot of new terms.

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And remember, you should feel like you
need to understand everything fully.

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Immerse yourself in the language, and
I will cover in detail what I believe you

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need to know at this point
of time in your learning.

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We're going to be using
workspaces again for this course.

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So you can follow along and

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code without having to install
anything at all on your local machine.

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We're also going to be making use
of a tool that might be new to you.

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It's called JShell, and it's the new
REPL that Java just got in Java 9.

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In case you haven't heard of
the term REPL or R-E-P-L,

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it stands for read eval print loop.

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And it allows you to interact with and
explore the language,

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I think you're gonna love it.

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Let's launch a workspace and check it out.

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Okay, so welcome back to workspaces.

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So down here in the console,
if you just go ahead and type jshell,

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it's going to start up,
it's gonna start the REPL up.

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So again, that's read eval print loop.

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Check the teacher's notes for
more on JShell.

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It's super powerful, and
it's up and coming, and

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let's use it right now to just refresh
ourselves on what we've learned so far.

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It's an awesome tool,
you're gonna love it.

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So what this will let us do, is it'll let
us create variables just like we know.

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So we'll do a string, firstName = "Craig".

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And you'll see what it does there,
is it says that it's set the variable

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name to Craig, it's kind of
that's its style of output there.

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So now we can access
those variables like so.

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So we'll say, isCraig, and
let's do this firstName.to

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call the method, equals("Craig"), right?

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So remember that, we call the equals
method on strings to check equality, and

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then it's stored in the variable.

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Now there's a variable called isCraig, and
you'll notice that I accessed firstName.

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So it's kinda in the scope of this
shell that we're working on here,

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pretty cool, right?

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You can also just go ahead and say,
firstName.equals(" Bob"), all right?

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And what that did,
is it created a new variable.

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Now there's a variable called $3,
and we can say it is $3 == true, and

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it doesn't, right, cuz we know.

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So $3 is a new variable name, and
now it made a $4 called false.

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So it just automatically
creates these variables, and

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it starts with $ in the front.

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It kind of just stores whatever is
returned, right, so if I do firstName,

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let's see, equalsIgnoreCase.

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Remember that that was the one
that allowed us to check,

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no matter if it was uppercase or
lowercase.

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So if I say, equalsIgnoreCase("CRAIG"),
it's gonna create a new, this $5 and

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it's in true,
just kinda stores whatever is there.

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So if you wanna refresh your screen,
you can do a Ctrl + L,

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and it will bring everything
up to the top, there we go.

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So if you did the extra credit on Java
basics, where we tried to validate input,

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you learned about the contains and
toLowercase methods that exist on string.

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Let's take a look at them real quick.

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So let's make a new string,
let's say string

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Some words = This is a bunch of WORDS,
all right.

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So we now have a variable
called someWords.

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And so, if I start typing S-O-M and
I press tab, it's gonna look, and

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it will search, and
it will find that I have someWords there.

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So it'll automatically do that,
and it works for methods too, so

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I'll do contains, and
I'll do tab and I'll pop this over.

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So contains looks for the word
bunch there, inside of some words.

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Does it exist?

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It sure does, there it is, all right?

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And we can also, if I press the up arrow,
things will come back.

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So then I can use the backspace there and
say, does it contain this?

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Which it does, right, there's this.

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So there's true, and
then also if I come and do,

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let's see if it has words in there.

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So this is case sensitive, right, so

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it doesn't contain words even
though it is actually there.

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So, we could create a new variable,
right, we could say,

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String loweredwords = someWords,
and remember this is toLowerCase().

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Yep, and
when there's multiple options there, so

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it's gonna show us the toLowerCase(),
that's what we want.

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So loweredWords, we could then check
if loweredWords contains words.

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And indeed it does, but
what if we did the method chaining?

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And remember this,
we could say someWords.toLowercase(), and

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instead of storing that variable,
we can just access it right here.

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It's called method chain,
remember we don't even need to create it.

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Cool, all right, so
we also did some work with integers, or

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whole numbers which were like this, right?

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So if we say int ageofBob= 30, and

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let's say that Mary, she's 28.

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And we could check and see,
I'm gonna put parentheses around these,

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just so, if Bob is older or
greater than the age of Mary.

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And I'm gonna do parentheses (ageofBob
is less than the age of Mary), right?

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I mean, that's how we talk about
numbers are greater than or less than.

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And finally, let's go ahead and,
remember when you get a number in,

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maybe you're getting in a number from
a program's coming in, you can parse it.

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So let's say that somebody
parsed in the string 30,

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you can get the number out with that,
there we go.

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And finally,
let's remember about Booleans.

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So using conditional logic like AND
or ORS, and

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those look like this in Java, so
you say, OR with a double pipe.

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So if we had say, false or false,
that's definitely going to be false.

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But what if we put a true here,
remember what happens?

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So the way that it works is, if any of
these are true, it means that it's true.

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And this is the case in OR, so it's like,
is this true, or is this true, or

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is this true and it is, so there's that.

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And then if we flip that around,
and again I use the up arrow, and

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I'm gonna remove these to be ampersands,
remember how this works.

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This is basically saying,
are all of these true?

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So is false and false and
true, so it's not true.

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And actually what's gonna happen,
is it's gonna shortcut.

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The second that it finds when it's false,

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it's not even gonna need to
look at the rest of them.

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So, and again, those could of course
be expressions like the age of Bob and

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age of many things.

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So, feel free to play around here until
you feel refreshed on what we covered.

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We'll spend quite a bit of time
in here during this course.

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And I'll show you a couple more cool
things that this awesome tool can do in

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upcoming videos.

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Now to get out of here,
you press Ctrl + D, cool and

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then you can do clear and
clear the screen.

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Awesome, I feel refreshed,

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that REPL is going to be super
handy going forward, right?

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Now before we get started,
I just wanna remind you that,

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during your learnings here.

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If anything at all isn't clear, or
even if you're pondering something,

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head over to the community and
share your question with everyone.

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By sharing your question,
it allows everyone to learn.

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And if someone else is
wondering that very same thing,

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it'll be answered when they
come to search for it.

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I can't stress this enough, the community
is awesome and supportive, and

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I've been blown away by
how quick answers appear.

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I can't even keep up,
you all are so great.

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All right,

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I think we're ready to dive into objects,
right after you ace this refresher quiz.