Java Parameters

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What if we need to provide some input data to our functions? In that case, we can add one or more parameters to the function declaration. Let’s look at an example.

In this code, we’ve added a variable declaration inside of the parentheses of our function declaration. In Java, we need to include both a type and a variable identifier.

Then, in our code, we can use that variable identifier just like any other variable. The value it will contain depends on the argument provided to the function when it is called.

For example, if we call the function foo() with the argument “Hello World”, that string will be stored in the message parameter inside of the function.

We can even take it a step further and look at a more complex example. Let’s walk through this code step by step and see how the data is shared between functions. As always, we’ll start in the main() function. First, we set the values for three variables, x, y, and z. Since those variables are declared in the main() function, we’ll need to list them under the main heading in our variable list.

Next, we’ll call the bar() function, using the variables x, y, and z as arguments. So, our program will look for the declaration of the function named bar(), and match up each argument with the parameter in the same position. That will cause the value in x to be stored in a, y in b, and z in c. Those new variables, a, b, and c, are declared as part of the function bar(), so once again we’ll list them under the bar heading in our variable list.

Once inside bar(), the code will print those values to the screen, and then the function will terminate and control goes back to the main() function.

Next, it will call the function foo() providing the variable y and the value true as arguments. Just like before, the program will find the function declaration for foo() in the code, and match up each argument with a parameter. So, in foo(), we’ll see that the variable output is given the value stored in y, and the Boolean longMessage is given the value true.

Adding parameters to our functions is a great way to make our code that much more useful. See if you can do the same in the example on this page.