Why do Programming Languages have methods ?

  • Methods are used to encapsulate (= put in a capsule) a series of operations used to solve a complex problem

  • Methods allow programmers to work with higher level of abstraction

  • Low level of abstraction = when we can see a lot of detail

  • High level of abstraction = when we can see less detail and the "big picture"

      • Abstraction is a commonly used technique to solve complex problems

Methods are useful, but not necessary for programming

  • Your life with methods: 

    public class WithMethod
{
   public static int sum( int start, int end )
   {
      int s = 0;

      for ( int i = start; i <= end; i++ )
         s = s + i;

      return s;
   }

   public static void main(String[] args) 
   {
      System.out.println("sum(1, 10) is:  " + sum(1,10) );     
      System.out.println("sum(25, 30) is: " + sum(25,30) );
      System.out.println("sum(40, 50) is: " + sum(40,50) );
   }

Methods are useful, but not necessary for programming

  • Your life without methods: 

    public class WithoutMethod
{
   public static void main(String[] args) 
   {
      int sum;

      sum = 0;
      for (int i = 1; i <= 10; i++) 
         sum += i;
      System.out.println("The sum of 1-10 is: " + sum);         

      sum = 0;				    
      for (int i = 25; i <= 30; i++) 
         sum += i;				      
      System.out.println("The sum of 25-30 is: " + sum);

      sum = 0;	
      for (int i = 40; i <= 50; i++)
         sum += i;				      
      System.out.println("The sum of 40-50 is: " + sum);
   }

    (Imagine doing this 1,000,000 times 😂)

Java method definition

  • Components in a method definition:

Using/calling/invoking a method

  • Invoking a method:

  • Very important:

      • The values of the actual parameters (= "arguments") are passed (= copied) to the parameter variables of the method

Java method definition

  • The signature of a method = method name + data type of the parameters

  • Java uses the method signature to select which method to invoke

Method overloading

  • Overloaded method = when there are multiple methods in the class with the same method name but different signature

    Example: 

       public class Overload
   {
      public static void meth( int x )
      {
   	 System.out.println("Running: meth( int x ) ");
      }
    
      public static void meth( double x )
      {
   	 System.out.println("Running: meth( double x ) ");
      }
    
      public static void meth( int x, int y )
      {
   	 System.out.println("Running: meth( int x, int y ) ");
      }
   }

DEMO: 02-review/Overload.java