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You have completed Java Loops!
You have completed Java Loops!
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Let’s explore the do-while loop, which guarantees your code runs at least once before checking the condition.
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If you're unfamiliar with Scanner, don't worry, it's taught in detail in an upcoming course. You can just follow along for now and consider it a sneak peak of what's to come.
Here is the Oracle documentation if you want to look into it further.
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Alright, welcome back.
0:01
In the last video, we entered the world
of while loops, Java's way of saying,
0:02
I'll stop when I feel it, meaning it runs
until the condition is no longer true.
0:06
We even had a little fun
with infinite loops and saw
0:11
how to break out of them
before our computers started smoking.
0:14
But now it's time to meet the while
loop's quirky cousin, the do-while loop.
0:18
If the while loop is the cautious type
that always checks before acting,
0:23
the do-while loop is the goofy one
that just does something first
0:26
and then asks, Wait, should I keep going?
0:30
It's like eating one of those cookies
0:34
and then checking
if you're supposed to be on a diet.
0:35
So what's the difference?
0:39
With a regular while loop,
0:41
the condition is checked
before the code inside the loop runs.
0:42
If the condition is false
right from the start,
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the code inside might never run at all.
0:48
But with a do while loop,
0:51
the code inside the loop always runs
at least once, no matter what.
0:53
The check comes after.
0:57
So even if the condition is false, you
get one guaranteed spin through the loop.
0:59
Let's get back into our workspace.
1:03
Let's open up do while dot Java
1:07
here and jump right into main.
1:09
So here's what the syntax looks like.
1:12
We'll say do, some curly braces,
1:14
and this is where we put the code
that we want to execute.
1:17
Then, after the closing curly brace,
we say
1:20
while and then add our condition
in some parentheses.
1:23
Don't forget your semicolon with this one.
1:26
So the regular while loop,
1:30
a do while loop is great for input,
output, and menus, because we typically
1:31
want our menus or prompts
to appear at the start no matter what.
1:35
Let's see it in action.
1:39
Imagine you want to ask a user
to enter a secret password,
1:41
and you want to keep asking
until they get it right.
1:45
So we need to make sure
1:48
the prompt shows up at least once,
or else they'll never be let in.
1:49
Here's how you could do that.
1:53
Let's import scanner up top again.
1:54
Then we'll create an instance of one here
1:58
in main and pass in system.in.
2:00
Perfect.
2:07
Okay, let's create a variable
for our super secret password
2:08
String password equals open sesame.
2:12
All right, now let's declare a variable
that will eventually hold their input
2:18
so we don't need to define it
with a value yet. String user input.
2:22
There we go.
2:27
Now what do we want to do?
2:28
Let's prompt
the user for the secret password.
2:29
system.out.print
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Enter the secret password,
and we'll leave a space there.
2:35
Then we'll assign
2:39
their input to our variable
with user input equals
2:40
scanner dot next line.
2:44
Cool.
2:47
Now we have to check their
input against the password.
2:49
We'll say not with that logical
not operator there, the exclamation mark.
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User input dot equals password.
2:57
If you're unfamiliar,
this is basically saying
3:00
if the user input
does not equal the password.
3:02
So while their input is not the password,
keep looping.
3:06
Then, after the loop closes,
we can say System.out.println
3:10
Enter if you dare.
3:15
Ok, let's test this out.
3:21
Enter the secret password.
3:34
Let's see if they're even aware
they have a password.
3:36
We'll try password.
3:38
Nope, that didn't work.
3:41
Let's try 12345.
3:42
Nope, they're good, they're good.
3:44
Oh I know!
3:47
Open Sesame.
3:48
Enter if you dare.
3:51
Perfect.
3:53
So the prompt will always show up
at least once,
3:54
even if the user just
nails it on the first go.
3:57
So to sum up, use the do while loop
4:00
when you want your code to run
at least once, no matter what.
4:02
It's perfect for things user input, menus,
or any time you want to guarantee
4:06
that your loop body gets a shot
before checking the condition.
4:11
As before, always make sure your condition
will for sure change at some point though
4:15
to not get stuck here forever
guessing the password for all eternity.
4:20
Okay, there's two other loops
you need to know about,
4:25
but first, do let this sink in
while it's fresh in your mind.
4:28
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