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Title:
Add or Remove Parameters
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Description:
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I'm going to walk you through
an example of a method with a different
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number of input parameters.
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I started by creating a new app from
the project wizard in Android Studio, so
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this is completely unrelated
to the Just Java app.
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I added this method
in the main activity.
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It's called createWeatherMessage.
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There's no input parameters, and
the return value is a string.
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This method is supposed to create a new
message that specifies the city name and
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the temperature.
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You can think of a method as
being a template of instructions.
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So I can make temperature
be an input parameter.
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And it's a number, so
I'm going to say, int temperature.
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And then I can use this right here.
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So, this is a string literal, and
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then it's concatenated with
the temperature integer.
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And then it's concatenated with another
string that says degrees Fahrenheit.
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So now the message can be customized
based on the temperature because it's
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an input parameter.
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Oh yeah, I forgot to mention this
earlier, but in the onCreate method of
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the main activity, which is called
when the activity gets created,
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I can call the createWeatherMessage.
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Before I passed in no arguments, but
now we have one required parameter.
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So I'm going to pass in 77 for
the temperature.
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Now that makes the error go away,
and this method call is correct.
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The other thing I should modify
is this comment on the method.
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I'm going to add a blank line, and
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then I'll start to describe the input
parameter which is temperature here.
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I'm going to type @param temperature,
and
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then I can add a description saying that
this is the temperature of the city.
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Sometimes the parameter names
are a little hard to understand, so
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that's why the description is useful.
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Other times if your method is public
then other people will be able
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to call this method, and
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they might not know what
are the instructions inside this method.
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So reading this java doc and
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the description of the parameters
is really useful to them.
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I mentioned earlier that
a method is like a template.
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So, what if we want to change the city
so that it's not always San Francisco?
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I can make city be an input parameter.
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So I can just add a comma here.
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And since city name is text I'm
going to make it a string data type.
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Then I can delete San Francisco and
replace it with a variable city name.
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And remember to add a space before and
after here as well.
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Cool, so
now this method can create a message
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that's customizable to
a certain city and temperature.
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I also remembered to
modify the java doc so
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that it has this extra parameter and
description for a city name.
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Since I changed the method signature,
now I have an error up here.
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The method no longer works
with just one argument.
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I need to pass in two arguments.
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So I add a comma and
then pass in San Francisco string.
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Now the error goes away.
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So when I call createWeatherMessage(77,
it's going to be value of temperature,
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and San Francisco will be
the value of city name.
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And it will create
the proper string here.
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Now we're going to go back to
the calculate price method,
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and we're going to modify
the method signature so
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that it has a different
number of input parameters.
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We're going to define it with zero
input parameters, one input parameter,
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and lastly,
try it with two input parameters.
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You'll see how changing the method
signature here to have a different
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number of input parameters with affect
the way that the method is called.
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Normally when you're building your app,
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you will just define it one way with
a certain number of input parameters.
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And usually that number of input
parameters is going to be determined
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based off of what's
happening inside the method.
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The best practice is to
only pass input parameters
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that you're actually going
to need inside this method.
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There's no point in passing over more
information if you're not going to
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use it inside here.
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Here are the instructions for this task.
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First define the calculate price method
in your app in the main activity.
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See the instrructor notes for
a code snippet that you can start with.
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We're going to modify
the calculatePrice method so
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that it only has one input parameter.
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Then in the submitOrder method
call calculatePrice and
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pass in quantity as the input.
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Then try to modify the calculatePrice
method to have two input parameters.
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That way in the submitOrder method you
will call calculatePrice quantity and
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then you can pass in the price
which could be $10 for example.
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And lastly, try changing calculatePrice
so that it has zero input parameters.
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That way in the submitOrder method
you would just call calculatePrice
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like this.
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Let's do the first one together so
you understand what I mean.
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I'm going to open up the link
in the instructor notes.
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In this gist we provided code for
the calculatePrice method.
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So go ahead and
select everything and then copy it.
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In Android Studio,
I'm going to paste in this method.
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I'm just going to paste it in
right below submitOrder, and
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I'll make sure that there's a blank
line in between each method here.
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That makes it easier to read.
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Then I can call this method
from the submitOrder method.
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I'm just going to insert the call
at the very bottom of the method.
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Later we're going to integrate
it with the code up here.
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But for now, this is good.
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Oops, I forgot that we have one input
parameter, so I need a pass quantity.
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Now do the same for
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the remaining two tasks by modifying
the input parameters here.
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To complete this task,
if you need examples to reference,
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you can always do a Google search for
Java methods.
