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Receiving Input
3:18In this video, we will "listen" to the user by accepting input from the keyboard. We will then use this input to dynamically change our output to the screen.
So now we have a way of
communicating with our users.
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However, our conversations seems
a little one sided, doesn't it?
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Let's see if we can't go ahead and
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listen to what the person on the other
side of the screen has to say.
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So what we've done thus far is all output.
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Now we're going to introduce
input into our application.
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More specifically input from the keyboard.
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Let's head back over to our workspace and
take some input.
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Okay, so our first named variable
here is currently hardcoded.
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Let's see if we can't make
it a little more dynamic.
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Remember how we said that objects
like console have methods
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that allow them to perform actions?
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So far we've only seen one method, printf,
and that prints text to the screen.
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Well the same console object that
we've been using has another method
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called read line.
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Just like the printf method prints text
out to the user, the readline method
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prints text out, and then it captures
whatever the user types afterwards.
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So it can be used to prompt the user for
their name and
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then capture what they type.
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Let's do that.
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So first let's remove the string.
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And then let's type console.
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And then we can access its
methods by pressing a period and
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then we'll type readLine,
that's the name of the method.
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And we'll call it double quotes, will type
what is your name, cuz that's the prompt.
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Two spaces and then a quote, and
then we will end the parenthesis,
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and we're gonna just leave
that semi colon there.
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Okay, so let's take a look at this.
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So like we said,
the read line method gives us a string.
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This is known as returning a value.
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We know that we can call methods
on an object to perform actions
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while another feature of methods is that
they can return back information when
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they're done performing.
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In this case this method
returns a value that we
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then use to set our first name variable.
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Just like before, we use that value stored
in the first name variable to write out or
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formatted sentences.
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Okay, so we're gonna save our file,
then we are going to compile javac
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introductions.java.
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And there we're gonna go ahead and
type java introductions and press Enter.
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And it's gonna prompt us know and see
because up at the two spaces notice how
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the cursor is right there
right after the two spaces,
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that's why it's important to leave
the two spaces in the prompt.
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So we'll say, what is your name?
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And we'll put in Andrew and we'll see the
program run and you'll see that it puts
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Andrew in all the places where the first
name variable was just like before.
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Now the program has dynamically changed
based on input from the user, nice.
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We've now learned how to take input from
a keyboard in a command line program and
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then output a formatted version.
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This combination of input and
output is often referred to as IO.
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In fact, if you look at the top
of the code that we just wrote,
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we're importing the console
type from the java.io package.
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Java packages are used to bundle
related functionality and programs.
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Building and using packages is
a more advanced concept but
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I just wanted to point out here that that
new term that you just learned about IO
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is already right there in the statement
that we had previously ignored.
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Congrats, you now know how to send output
receive input, store and use variables.
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You will use these concepts in
almost every interactive application
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that you'll write.
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Now since they're such important concepts,
let's end this stage with an exercise.
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