Functions/Methods

Modern programming languages are very small, but they allow you to extend the language by creating new command words.
In Java, a new word is called a function or method. Functions are a powerful way to keep your code readable and easy to maintain.
A function is an abstraction: it does something, but you don't have to know how it does it in order to use it.
You can think of a function as a machine. All machines have some function (do something):

• Some machines (like a meat grinder) require input of raw materials and output (return) processed materials.

• Other machines (like a music box) produce output (music) without any specific input.

• Still other machines have neither inputs nor outputs but affect other things (like pressing the button on your car remote control)

Every Java function has 4 primary characteristics:

• a name followed by parentheses

• optional inputs (called parameters) placed inside the parentheses

• a body (the code that defines what the function does)

• an optional output (called a return value)

Consider the following function:

  int square(int a) {

       return a * a;

   }

• The function's name is square (notice that function names are typically verbs because they do something).

• It takes an input parameter that is an integer and is referred to within the function as a.

• The function returns an integer that it computes by multiplying a by itself.

You could use the square function as follows:

  int a = 9;

   int b = square(a);

The two pieces of code above can be used to create the following program.

public class function {

    static int square(int a) {

        return a * a;

    }

    public static void main(String args[]) {

      int a = 9;

      int b = square(a);

      System.out.println("b=" + b);

    }

}

Functions can take more than one parameter, but they can only return 1 value (or no values). Consider this function that takes two input parameters and returns no value:

  void echo(String msg, int times) {

        for (int n=0; n<times; n++) {

            System.out.println(msg);

        }

   }

Create a new EchoExample project folder and in it create an Echo program as follows:

public class Echo {

    static void echo(String msg, int times) {

        for (int n=0; n<times; n++) {

            System.out.println(msg);

        }

   }

    public static void main(String args[]) {

        echo("howdy", 10);

    }

}

• Save the program as Echo.java

• Run the program and observe the output

• For now, we're going to ignore the keywords public and static, we'll get to those soon