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Most functions rely on parameters to perform their task.

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Functions with parameters expect to receive a values.

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Functions without parameters.

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Do not expect to receive any values.

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In this lesson, you will create a function that defines parameters.

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First create a new file named Parameters Java and make sure the class has a main method.

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The area of a rectangle, as you know, is equal to length times width.

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You've been given three rectangles and each rectangle has different dimensions.

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Our job is to calculate the area of each rectangle.

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How will we do this?

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Step one is to create a function that expects to receive a length and a width.

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Here I have a function called calculate area.

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The function expects to receive two double values a length and a width.

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A parameter store is a value that your function expects to receive.

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The function calculate area defines two parameters.

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Therefore it expects to receive two values.

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The next step is to call the function by passing in an equal number of values.

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In order to call the function calculate area, you need to pass in one value for every parameter that

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it defines.

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A value that you pass into a function is known as an argument.

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The function calculate area defines to double parameters.

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Each parameter expects to receive a double value.

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So in order to call the function, you need to pass in to double values.

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The actual values that we pass in are called arguments.

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In step three, the function uses its parameters to perform a task.

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The function calculate area uses its parameters to calculate an area.

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If we were to trace the runtime first we're calling calculate area.

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The values that we pass into the function are arguments.

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When the function gets invoked, the first parameter stores the first value that was passed, then the

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second parameter stores the second value that was passed in.

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The function uses the value inside each parameter to perform its task.

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It calculates an area and prints it.

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You might be wondering why is this beneficial?

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Think about it.

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If you want to calculate the area for three different rectangles, I can just call this function three

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different times each time passing in a different set of arguments.

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If I call the function and pass in these values, the first parameter stores the first value that was

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passed, then the second parameter stores, the second value that was passed in the function uses the

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value inside each parameter to calculate an area, and it follows that the function can calculate an

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area for any pair of values that get passed in.

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The function is completely reusable.

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Let's do this in code, starting with step one, creating a function that expects to receive a length

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and a width.

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All right.

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Our function is going to be publicly accessible.

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It will be void.

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It's not going to return any values.

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We'll talk about return values in the next video.

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And we're going to call the function calculate area.

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Our function calculate area expects to receive two values.

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So we need to define two parameters double length and double width.

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Think of a parameter as a variable that just stores whatever value gets passed into our function.

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So a double length will store the first value that gets passed in and double width will store the second

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value that gets passed in.

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Task two is to call the function by simply passing in two values.

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I'm going to call the function calculate area.

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And the reason this is not auto completing is you'll remember the function calculate area needs to be

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static as well in order for it to be called from the static main function.

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Don't worry about what static does.

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We will talk more about static in module two object oriented programming.

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For now, just know that we need to have it in order to call this function for main.

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And now I'm going to calculate the area for a rectangle with a length of 2.3 and a width of 3.6.

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The values that I'm passing in are called arguments.

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The variables that will end up storing these values are called parameters.

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It's really important that you make that distinction.

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In step number three, the function is going to use its parameters to perform a task.

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So when this function is called, it's going to receive two values where each value gets stored inside

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of a parameter.

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And now we can use the parameter values to calculate an area.

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Double area is equal to length times width.

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And after we calculate the area, we can print it.

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System, dot, dot, print line.

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The area is equal to the area that we calculated and we are done.

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And now, instead of running our code the normal way, we will visualize the runtime as we've been doing

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in the workbook solutions.

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So I'm going to put a breakpoint here and that's it.

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And now you'll remember that for this to work, for us to be able to visualize the runtime, you need

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to launch the exact folder that contains your Java file, in this case, section four.

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And now we can press debug to visualize the runtime.

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And in order to step inside the function that I'm calling, I need to press the button, step into.

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All right, so I'm calling the function calculate area, passing in two values, passing in two arguments.

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The first parameter length stores, the first value that was passed in the second parameter stores,

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the second value that gets passed in.

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So now length equals 2.3 and width equals 3.6.

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And to further prove to you that parameters are essentially just variables, press this button and you

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can visualize the length variable and the width of variable.

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And now we can use the values inside of each parameter, the values inside of each variable to calculate

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an area for a rectangle with a length of 2.3 and a width of 3.6.

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And the area for such a rectangle is 8.28.

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Once you reach this line, do not press, step in to press, continue to resume execution naturally.

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And the area for a rectangle with such dimensions is 8.28.

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What's beautiful about this is that the function is reusable.

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I can call it as many times as I want to calculate the area for any rectangle that I want.

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I can calculate the area for a rectangle with a length of 1.6 and a width of 2.4 for a length of 2.6

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and a width of 4.2.

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It doesn't matter.

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I can reuse the function as many times as I want to, and this is a really, really powerful way of

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coding.

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All right, let us visualize the runtime once more.

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So here I'm calling the function calculate area and line number three.

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I'm going to step inside the function that we're calling the length parameter stores.

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The first value that was passed in the width parameter stores, the second value that was passed in.

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I will keep stepping into the function.

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The area based on the values that were passed in is equal to 8.28 and now do not make the mistake of

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pressing step into because then it's going to step into the print line function, which we don't want

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to do press step over to run this line.

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And the area is 8.28.

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And now if I want to continue to the next the breakpoint, I can press the continue button.

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All right.

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Now I'm calling the function again, passing in a value of 1.6 and another argument that equals 2.4,

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stepping into the function that we're calling the first parameter stores, the first value that was

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passed in the second parameter store is the second value that was passed in.

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And now we're calculating an area based on the parameter values.

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If I keep stepping into area equals 3.84.

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Don't make the mistake of pressing step in because then it's going to step into the print line function,

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which we don't want to do.

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We will step over this line and it prints area is equal to 3.8 for continuing to the next breakpoint.

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Stepping into the function again, the length parameter equals 2.6, the width parameter equals 4.2.

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We calculate an area based on these parameter values and then we can print the area.

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10.92.

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And now if I press continue because there are no other break points that come after the run, time will

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just terminate.

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Beautiful.

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So to recap, a parameter store is a value that your function expects to receive.

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When a function defines parameters, then in order to call it, you need to pass in a matching number

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of arguments based on the position of the parameter.

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It's going to store the value that gets passed in, and then we can use these values to perform our

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task.