Java Chapter 7 - Writing Methods

7.1 Basic Methods

Within a class, you can have many methods (functions). You may create methods to put code into reusable containers. Putting code in methods can also make the main program simpler and more readable. Below is an example program with three methods.

methods.java

public class methods
{
   public static void main (String[] args)
   {
      PrintIntro();
      PrintConclusion();
   }

   static void PrintIntro()
   {
      System.out.println("This is the introduction");
   }

   static void PrintConclusion()
   {
      System.out.println("This is the conclusion");
   }
}

Output
This is the introduction
This is the conclusion

When your primary class has multiple methods, the entry point of the program is the method named main.

Static keyword: The word "static" means that the method can be used without declaring an instance of the object (class). This is usually the case for methods used as functions in the main class.

7.2 Methods that Send and Return Data

The program below demonstrates using a method that you send data to and returns a value.

paycheck.java

// This program demonstrates sending data to a method and returning a value.

public class paycheck
{
   public static void main (String[] args)
   {
      double Hours = 4.0, Wage = 9.0, TotalPay;
      TotalPay = CalculatePay(Hours, Wage);
      System.out.println("Total Pay = " + TotalPay);
   }

   static double CalculatePay(double Hours, double Wage)
   {
      return Hours * Wage;
   }
}

Output
Total Pay = 36.0

Let's examine the format of the header line of the CalculatePay method:

public	static	double	CalculatePay	double Hours	double Wage
public: Any class can access this method. private: Only other methods in this class can access this method.	With this keyword, this method can be used without declaring and instance of the object/class.	The method returns a number of type double. If the method doesn't return data, this should be void.	The name of the method.	Declare a variable to store the first parameter.	Declare a variable to store the second parameter.

7.3 Access Modifiers (default, private, public, protected)

Methods and class variables have 4 access modifiers.

1. default - If you do not add an access modifier, it is the default access modifier. The method or class variable can be accessed from the package only.
2. private - The method or class variable can only be accessed from within the class.
3. public - The method or class variable can be access from anywhere.
4. protected - The method or class variable can be accessed from within the class or subclass, but not outside the class.

7.4 Overloading Methods

You may define two or methods that share the same name within a class, as long as the parameters are different. The parameters can be different in type and/or the number of parameters. For example, you could have methods that calculate the average of numbers.

overload.java

// This program demonstrates overloading methods
// If you call Average() with 2 parameters, the first method is used
// If you call Average() with 3 parameters, the second method is used

public class overload
{
   public static void main (String[] args)
   {
      System.out.println( Average(5,10) );
      System.out.println( Average(5,10,15) );
   }

   public static double Average(int A, int B)
   {
      return (double)(A + B) / 2.0;
   }

   public static double Average(int A, int B, int C)
   {
      return (double)(A + B + C) / 3.0;
   }
}

Output
7.5
10.0