Calling Functions

A function call is how we tell our program to execute the code in a function's body. We've already written plenty of function calls: the statements println("Hello, World!"); and String name = nextLine(); both contain function calls. A function call has two parts:

• A function call begins with the function's name.
• A function call includes a list of argument in parenthesis after the function name, or a set of empty parenthesis if the function requires no arguments.

The argument list in a function call is a list of values to use when initializing the function's parameters. Let's consider the add function defined in the previous section:

double add(double x, double y) {
    return x + y;
}

We can't run the code x * y without first initializing x and y. If we call add, then we need to provide an initial value for each parameter: add(2, 3). The first argument is used to initialize the first parameter (x), the second argument initializes the second parameter, and so on. You may hear the terms "argument" and "parameter" used interchangeably because they're both referring to a function's inputs. It's usually clear from context what we mean when we say "argument" or "parameter", so don't worry about getting them mixed up. You may also see the term "formal parameter" used to refer to the parameters in the function's definition and the term "actual parameter" used for the values supplied with a function call.

Examples

If we want to call the functions defined in the examples from the previous section, we would write:

// will print "Hello, World!"
sayHello();

// will print "Hello Zach, how are you doing today?"
greetPerson("Zach");

// will set x equal to 16
int x = square(4);

// will print 16
println(x);

// combines the previous two statements into one step; will also print 16
println(square(4));