Method definition is composed of the following formula (see method Header see: page 272) is composed by:

<encapsulation type><modifiers><return type><id>(<parameter data type><id>, ...)

where the following items:

• encapsulation type: this is the visibility of the method according to the scope of the class or the package.

  • public

  • private

  • protected

  • package (will not be used in methods only in classes in CS II)

• modifiers: allows you to perform operations inside/outside the class. It allows you to overwrite methods and overload

  • static

  • final

  • abstract

  • interface

• return type: what this method "gives back" once you called the method.

  • Eight primitive types (int, short, long, float, double, char, boolean, byte)

  • Object, e.g., String

  • void

• Id: the name of the method

  • An identifier that makes the method meaningful (camel case style)

• For parameters (if available): these are the values that are inside the parenthesis

  • Data type: i.e., eight primitive types, any object (e.g., String)

  • Id: the name of the parameter

E.g., Consider the functions from pre-calculus that you needed to solve back in middle school

f(x) = x2 + 3

f(2) = (2)^2 + 3

  =  4 + 3

  = 7

f(x) = x2 + 3

• If I called the function with f(2), I would get: 7

• Name of function: f

• Parameter: x

• The data type of the parameter: int

• What will the function return once evaluated: an int

By using the previous components mentioned above, we obtain:

public static int f(int x) // method header

By elaborating the body of the method: Notice that we state that our returning data type is an int; it is recommended to create a place holder for that and return it immediately as follows:

public static int f(int x){

int result = 0;

return result;

}

This way, your code can compile without any problem. Not the remaining piece of code is the actual calculation of the function (i.e., x2 + 3). We can simply make the statement in Java as "x * x + 3", resulting in the following method:

public static int f(int x){

int result = 0;

result = x * x + 3;

return result;

}

How can we call the method in Java? 

public static void main(String [] args){   

for(double x = 1; x <= 20; x+=0.1){

   double y = f(x);

   System.out.println("f("+x+"): \t"+y);

}

}

Method overloading

We can provide flexibility to the computer user to choose whatever option he/she wants to use. The method f takes an int as a parameter, but what about if we would like to provide a double? We can have another method with the same name but with a different header. The header is the part of the method that will provide the parameter data type. For example:

public static double f(double x){

double result = 0;

result = Math.pow(x,2) + 3;

return result;

}

Noticed in this version, we exercise the invocation of the Math.pow() method. This is an example of how to invoke methods inside of another method.

How can we define a method in Java? 

To guarantee a successful compilation and successful execution of your program, we recommend doing the following steps. We are going to keep using the function f(x) as an example:

1.  Identify all the elements of the

2.  Move outside the scope of the main, but stay inside the scope of the program

public class MethodExample01{

public static void main(String [] args){  

}

public static int f(int x){   

}

}

3. In order to compile your program successfully. You must return the data type that you claim you will use in the method header

public static int f(int x){

int result = 0;

return result;

}

4. For the rest, use the variable that you declared internally to perform operations; in this case, will perform the actual operation of f(x)

result = x * x + 3;

5. Combine Step 3 and Step 4 in the method:

public static int f(int x){

int result = 0;

result = x * x + 3;

return result;

}