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You have completed Java Basics!
You have completed Java Basics!
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In this video, we will learn what a variable is, and when they should be used. We will modify our introduction to dynamically use a String variable.
It's not an error!
Not to worry, the Picked up JAVA_TOOL_OPTIONS: -Xmx128m is not an error on your part, we recently just tweaked our setup to have more memory allocated. Don't fret that mine looks different!
Additional Info
- Other escape sequences
- More data types for the impatient
- Statically and strongly typed described (the first paragraph)
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So let's take a closer look
at what we just achieved
0:00
especially around the text
we printed to the screen.
0:02
We're going to learn about two new topics,
strings and variables.
0:06
In Java, by placing letters or
0:11
characters in double quotes,
we create what is known as a String.
0:13
A handy way to visualize strings,
is by picturing a banner that you might
0:18
hang at a party, that is stringing
together individual characters.
0:21
Strings are how we deal with text and
0:26
you'll encounter them quite a bit
in your programming adventures.
0:27
In fact, since strings are so
0:30
common, they're one of the basic
data types that Java offers.
0:32
A variable is a way to store data into
a named location that you can use
0:36
to reference later.
0:41
In Java, you must specify what data
type you are planning on storing so
0:43
that it knows how to store that
information, String is one of those types.
0:47
And we'll discover more data types as this
course progresses, when you need them.
0:52
If you just can't wait, I've also
added a link in the teachers' notes.
0:57
Let's go back to our workspace, and
let's learn how to use a String variable.
1:01
All right, so let's say I asked you to
write out another line to the screen that
1:07
said, Craig is learning how to write Java.
1:10
It looks something like this,
1:13
it's console.printf(''Craig is learning
1:16
how to write Java'');,
now let's save that.
1:23
Let's go ahead and
compile and once again we do,
1:30
javac Introductions.java,
1:32
that creates the class file and
we say, java Introductions.
1:39
Well, that output looks a little bit ugly.
1:46
It can definitely be prettied up by
putting that information on different
1:48
lines, but how are we gonna do that?
1:51
Now obviously,
if I press Enter in a line like this,
1:53
it's gonna probably break the program.
1:56
So what we have is there's a new thing
they introduced called an escape sequence.
1:59
And that is a \n.
2:05
And that is the new line escape sequence.
2:06
I'm gonna put that at the end
of both of our lines and
2:09
escape sequences are used to write
characters that are not easily printable
2:12
or may break the syntax or
the structure of our code.
2:16
Let's go down here and
let's clear the screen.
2:20
And you can do that by typing clear and
we'll clear our terminal.
2:23
See, it's reset back now and
let's go ahead and let's compile.
2:26
Now I want to show you another
little terminal trick here.
2:29
If you press the Up arrow,
it's going to go and
2:31
go through the history
of what you've typed.
2:34
So let's get back to where we said,
javac Introductions.java.
2:35
We’ll run that, whoop,
look I forgot to save.
2:39
You come up and you press Save.
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No, again let's go Up arrow.
2:45
Introductions, and
let's run it, here we go.
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That is much better looking and aside from
talking in third person Tarzan speak,
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this is looking much better.
2:57
All right, so let's assume we wanted to
make this program about someone else.
2:59
And one way to handle that would
be to change every String that
3:03
contains your name.
3:05
But imagine that our
program got much longer and
3:06
the name Craig is in hundreds of
thousands of places in the code.
3:09
We wouldn't want to have to
change that name everywhere and
3:12
keep changing it everywhere.
3:15
So a better way to handle this is to
store that information in what is known
3:16
as a variable.
3:20
So the way that you declare a variable
is first by defining its type.
3:22
And since we know we want to have
a string variable, say String.
3:26
And next we want to give it a name that
we can reference in the code later.
3:32
The better we name our variables,
3:37
the more likely someone reading our code
will be able to understand its purpose.
3:38
So in that case,
let's name our variable firstName.
3:42
Now we do an equal sign, and
then double quotes, and your name,
3:47
and then of course a semi colon to
mark that this statement is over.
3:51
This reads as assign Craig to
the variable firstName of the data type String.
3:57
In Java, while not required,
the standard for
4:02
naming variables is to use
what is known as CamelCase.
4:04
The first letter is lowercase, and
4:07
then each new word starts with
a capital letter, like this.
4:09
thisIsAnExampleOfCamelCasing.
4:14
Earlier when I introduced you to
the printf method on the console object,
4:21
I said that it was for printing text.
4:24
But, to be more accurate,
4:26
it actually prints formatted text
that's what the f stands for.
4:27
This lets us be more creative with
our text, using variables and
4:31
other special formatting instructions.
4:34
It turns out that printf takes
multiple options or parameters.
4:37
The first parameter that is
passed to the printf function
4:41
is what is known as the format string.
4:44
When using methods, you can add additional
parameters by separating them with a coma.
4:47
Those additional parameters are used
to replace the format specifiers
4:52
that are in the format string.
4:55
Let me show you what I mean.
4:57
First I'll replace Craig with the format
5:00
specifier %s where s stands for string.
5:04
And then, after the first parameter here,
I'm gonna insert a comma,
5:09
then I'm gonna put in
a firstName variable.
5:14
Let's do the same for the second sentence.
5:18
So we'll replace the Craig with %s.
5:19
And we'll get to the end of the line here,
and
5:22
we'll put a comma in the second
parameter argument is firstName.
5:24
Okay, so let's save that.
5:31
Let's do a clear,
we'll use the Up arrow to get
5:34
back to our javac Introductions,
so we'll compile the program.
5:39
We'll run the program,
great it still works.
5:43
Okay now let's change the value of our
firstName variable to a friend of yours.
5:49
I'll change mine to a fellow
teacher's name, Ben.
5:53
And I'll save the file and
we'll do clear, run javac and
5:57
then we'll run Java and
we'll see that I only
6:03
changed the one place,
but we updated both lines.
6:07
Great job using strings and variables and
formatters even, for that matter.
6:13
So we learned, when you create or declare
a variable, you first use its data type.
6:18
In this case, we used the data type string
and then we assigned with the equal sign
6:23
and set the firstName variable
to the String, Craig.
6:29
We created that String by
surrounding it in double quotes.
6:33
And of course we end our
statement with a semicolon.
6:38
So that is the syntax or
structural rules for creating a variable.
6:41
One thing of note here is that Java is
case sensitive which means the case,
6:46
is it upper case or lower case?
6:51
It makes a difference.
6:53
Now let's do an exercise and make sure
all this new information is sticking.
6:54
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