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We will wrap up exploring how to pass arguments into your Java application as the program starts. We will have a well deserved introduction to the basics of arrays and how to access their different elements.
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It's hard to believe we've made it this
far without actually directly talking
0:00
about arrays.
0:03
We've definitely seen them, and
0:04
in fact as we saw briefly strings
are just an array of characters.
0:05
Arrays are basically ways to store
multiple items in a single variable.
0:10
You can get access to the different
elements in the array and
0:14
you can use other properties
that help you loop through them.
0:16
You can plan to learn more about these and
other data structures in upcoming courses.
0:19
I'm introducing this to you now however
because it's the last part of the Java
0:24
boilerplate code that we have to go over.
0:28
So we want to pass in the puzzle phrase
when we call our hangman program.
0:30
This is done by passing in an additional
argument to the Java program,
0:34
here let me show you how to do it.
0:38
All right so let me show you how
to make one of these arrays.
0:40
So we'll make a single variable so I'll
do string, and then we're gonna do these
0:44
brackets, open bracket, close bracket and
we'll call that fruits.
0:48
And an array literal starts with
a curly brace on some languages it
0:52
uses the indexing thing there but
Java we use the curly braces.
0:57
So just be careful there,
banana and cherry.
1:02
And now we'll have this thing,
this object.
1:09
It's a single variable but
we can access it by different indices.
1:11
So arrays are zero index based,
so the first one is zero.
1:16
So if I do fruits[0] I'm
gonna get back "apple".
1:20
Cool, and I can also have, there is a
property on these called fruits.link that,
1:24
show me how long my array is.
1:29
So there's three entries there, now, for
more on arrays, check the teacher's notes.
1:31
But what I want you to see right now is,
look at how this is declared.
1:35
And see this is declaring
an array of strings.
1:38
And if we look at our main method here,
it's an array of strings.
1:41
So what we wanna do is we wanna make
sure that somebody passes in a value.
1:45
So, let's do that, so we'll say,
if args.length, right.
1:49
So we know that it's an array that
has something if it's equal to == 0,
1:54
means they didn't pass something in,
right.
1:58
And what we'll do is we'll warn them,
2:00
we'll say System.out.println("Usage:
2:02
java Hangman, and
then we'll just format like this.
2:09
This is kinda standard command line CLI
sort of things so we'll say system.
2:14
There's another thing we,
2:20
have out and in, we also have an error and
this'll be a little bit louder.
2:21
So ("answer is required") is
the error that we're gonna send.
2:26
And then, I don't know if you
remember this or not, but
2:30
we can exit out of our program
by saying system.exit(1).
2:32
And now none of the rest
of this will matter.
2:34
So now we know that we have,
a value in args, if we get here we know.
2:36
So we're gonna,
instead of treehouse let's go ahead and
2:42
let's use args[ 0], cuz we know
that there's at least one there.
2:47
So now if I try to start this program and
I don't specify it,
2:52
I'm gonna go ahead and get out of here.
2:56
So let's go ahead and we'll say clear and
2:59
Hangman.java, and java Hangman and
3:04
I didn't specify anything
there at the end.
3:09
So is gonna tell me that I made a mistake.
3:14
Oop, so there is it is so Usage: java
Hangman is required answer is required.
3:18
Awesome, so we block it, so
let's apply a parameter.
3:23
So I'm gonna use the up arrow and
here we go.
3:30
And now we have to guess
what you actually are
3:32
P-R-O-G- A-M-E.
3:38
Programmer, you did it, one more
thing I wanted to show is, look how
3:47
the class here is declared as public, this
hangman class is declared as public and
3:51
you've probably seen that in all
the classes that we've done.
3:56
Now typically this is
something that you wanna do.
3:59
If you refer back to the access level
modifier table that I shared in the very
4:01
beginning of this course you'll see that
classes actually fall under the same
4:04
access that fields and methods do.
4:08
So if we wanted a class to be used
outside of it's package, right.
4:10
So right now it doesn't have any
declaration or other classes here, right,
4:14
or prompter.
4:17
And our Java just says class, anything
outside the package couldn't access it.
4:18
So we should really be professional and
put public in here.
4:22
Now I did that because
there's a little trick with
4:27
Jshell that lets you import the classes
if you don't put public there.
4:30
So that's why we did that awesome,
so now it's labeled properly.
4:33
You know how arrays work,
you can play this.
4:37
Glad we finally got to go over arrays.
4:41
You'll end up using these a lot and
we'll talk about those and
4:43
more handy ways to structure
your data in upcoming courses.
4:46
You've learned a ton and I love that we're
now at a place in our learnings where we
4:49
don't need to ignore things in
the boilerplate code anymore.
4:53
Let's look at it one more time just to
show you what a good grasp you have on it.
4:56
So again when we run the Java
program we pass it a class name.
5:00
What that does is it looks for
a public method named main in that class.
5:05
Because it is a class method
not a instance method
5:10
it is marked with the keyword static.
5:13
The method doesn't return anything at all,
so its return type is void.
5:15
It then takes any arguments it was passed,
5:19
you can pass multiple
arguments with spaces.
5:21
It puts together an array of strings and
5:23
then passes that as an argument into that
method which you can access through this
5:25
parameter here called
args in your program.
5:30
Pretty cool right.
5:32
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