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