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You have completed Java Basics (2014)!
You have completed Java Basics (2014)!
Preview
In this video, we wrap up the course by introducing a mechanism to continually prompt until a valid response is obtained.
Learn more
- This is a very short introduction to loops. Some of your fellow classmates contacted me and asked for more. If you want more too, I did a live workshop called Feeling Loopy with Java.
Extra credit
- There is a method on string called
contains. It checks to see if one string is contained within the other. This seems like a good way to build a master list of words that are not allowed. Why don't see if what they typed is in a long string of bad words. - After you get that working, attempt to take case into account. If your list of bad words that you maintain is all lower cased, you can check the lower case version of the input in the bad string. How do you make a string lowercase?
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At the end of the last video, we talked
about how it was frustrating to do such
0:00
a hard exit when there was a word that
was entered that we wanted to censor.
0:04
It's probably, in fact,
0:07
much better if we continue to prompt
the user until we get a proper value.
0:08
This is a common pattern in programming.
0:13
And it's usually solved using
what is known as a while loop.
0:15
Now what happens is you run the same
code block until a certain condition
0:18
is no longer true.
0:23
In other words, while this
condition is true, do these things.
0:24
Java has a nice feature called a do while,
0:29
which allows us to first run the code
once before any live checking is done.
0:32
Let's use the do while loop to make
sure that the user enters a valid word.
0:36
Okay, so the first thing we wanna do is
locate the block that we wanna repeat.
0:41
So like we said, we wanna continuously
prompt the user until we get a valid noun.
0:46
So it looks like here is
a good place to start.
0:50
So in order to repeat the code,
what we'll do is use the keyword do, and
0:56
then we'll do an open bracket there,
1:00
which that signifies that
there's a new code block coming.
1:03
I'm gonna highlight these.
1:07
I'm gonna press the Tab key.
1:08
Great.
1:11
Okay, so now what we want to do is,
we want to change the exiting text,
1:12
because we're no longer gonna exit.
1:15
So let's come over in here, and
we'll change this to say try again,
1:17
and then we'll get rid of the System.exit,
because there's nowhere we're gonna exit.
1:22
Okay.
1:29
So next what I'm gonna say now,
because we're in the do loop code book,
1:30
and then we're going to put in while.
1:36
All right and so now, we are gonna loop
while these things are invalid, so
1:40
we already have a statement for
this which is that and I will do, and
1:44
then we'll do this and
we'll end in semi colon.
1:50
All right.
1:55
Now I hope that is starting
to feel wrong to you, and
1:56
that you just I thought that said wait
a second, you said don't repeat yourself.
1:59
Well don't worry,
we'll fix that in the minute.
2:03
So in addition to repeating ourselves, I
just introduced a bug into this code, but
2:05
I want you to experience it as it's
very common and knowing how and
2:09
why to fix it will save you loads of time.
2:13
Okay, so let's go ahead and
save this and let's compile it, and
2:16
we'll get an error here.
2:20
OK, so it says error cannot find symbol,
and it's pointing here to noun.
2:22
That's interesting cause we very clearly
define noun here and set right here,
2:29
set inside of this block
instead of this two block here.
2:33
The problem arises,
because of something called scope.
2:36
Every time we open up a block of code,
like we do right here.
2:40
It opens up a new variable scope and
code run outside of the scope.
2:45
So see here's the closing here, and
here's the noun that we're using and
2:50
see it's outside of that scope.
2:54
So everything that runs outside
of that scope can't see
2:56
the variables declared inside.
2:59
Now the reason for this, and why you might
want to use this is a more advanced topic.
3:01
And we'll get into that
later in a further course.
3:04
But for now, I'd like to assist
you in solving the current problem
3:07
of the outer scope not
knowing about the variable.
3:11
And it's actually pretty easy.
3:14
What we want to do is we just want
to declare the variable outside.
3:15
So we'll say String noun.
3:19
And then we want to remove
the declaration here,
3:23
because we want it to be talking
about the same variable.
3:25
All right?
So declare it here, and
3:28
then we'll use it here.
3:30
Okay, so let's try that out.
3:32
I'm gonna save.
3:34
Let's compile and run.
3:37
Great.
3:40
Okay, so let's see, dork, the language
is not allowed, I'll try again.
3:44
Jerk, no?
3:49
Awesome.
3:53
Okay so now back to that bad practice
we introduced of repeating ourselves.
3:55
So what tool do we use when we want
to store a value and reuse it?
4:00
That's right, a variable.
4:04
We can evaluate and store the results of
the condition that's in the if statement
4:06
and store that in a variable.
4:10
As we said earlier that's
called a boolean value.
4:13
A boolean is a primitive data type and
it starts true or false, and
4:16
it uses the lower case convention.
4:19
Let's declare our variable.
4:21
That's boolean isInvalidWord
4:26
equal, I'm wanna go ahead and
4:30
use the same trick that we did
before with the parenthesis.
4:32
So I'm gonna copy that.
4:39
Same here.
4:43
See if we can make that
look a little bit cleaner.
4:45
That looks pretty good.
4:50
So now we can use the boolean.
4:52
We can say if is invalid word,
4:54
we can use that boolean here
that code that we duplicated.
4:57
And we also notice something else.
5:09
We notice we're defining
inside of the scope here.
5:11
We're defining a boolean, but when we
are using it outside of the code block.
5:14
What do we do?
5:18
We're going to go ahead and do what we
just learned and move this boolean,
5:18
put it up here.
5:21
Great.
5:28
Go ahead and save, compile,
let's make sure things are still working.
5:30
Great it is excellent.
5:34
I think we have a fully
censorship ready prototype.
5:43
Awesome job adding loops to your skillset.
5:47
Now we know how to continuously run our
code until a specific condition is met.
5:50
I'm certain that you'll end up
using this pattern quite a bit.
5:54
We also learned that we can use a do while
loop to make sure that the code runs at
5:58
least once first before looping.
6:01
There are other types of loops that
will investigate in future projects, but
6:04
the basic idea is the same for
all of them.
6:07
We store the results of a condition in a
boolean variable, so that we can reuse it
6:10
and not repeat ourselves in code,
and thus keeping things dry.
6:14
We came up with a user
friendly way to censor input,
6:18
without causing the users to restart or
lose data.
6:21
I'm quite happy with where we ended
up after soliciting feedback from
6:24
our beta testers.
6:27
I'd like to congratulate you here.
6:29
We have a working prototype.
6:31
I'd like to encourage you to show it
off to your family and your friends.
6:33
You should practice by
making the story longer.
6:36
Add different parts of speech and
experiment with other ways of censoring.
6:38
Share your findings with the community.
6:42
I've added a couple of suggestions of
directions that I'd like you to explore in
6:44
the teacher's notes.
6:47
There are better ways to solve some of the
problems that you're likely to run into.
6:49
We just haven't gone over them yet.
6:53
But the point is this, you created
a working application, and you immersed
6:54
yourself in the Java language,
and you did an awesome job at it.
6:58
I hope you had a fun time doing it.
7:02
I look forward to walking through our
next problem introducing you to more and
7:04
more tools and concepts.
7:07
Thanks again for hanging out,
and I'll see you next time.
7:09
After the exercise of course,
7:12
you didn't think I was going to let
you go without a challenge did you?
7:13
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