Object Oriented Programming

OOP = programming paradigm. some defns:

• class = blueprint in code (e.g. a bicycle class might have a "speed" variable and a speedUp() method)
• object = instance of a class (e.g. Ronnie's bike)
• abstraction = means hiding what isnt important when working with classes / OOP
• encapsulation = techniques to bundle and hide methods and properties within classes (e.g. using public and private keywords). this is one way to enable abstraction
• inheritance = when new objects to take on the properties of existing objects (e.g. a circle object inherits the properties of a shape object)
• polymorphism = ability for an object to take on many forms (e.g. a method draw() could be used with triangles, stars and boxes)

Player class

a player has a username. if a username isnt supplied when creating an instance of this class, the username is set to "unknown" by the constructor when the object is first created:

//save as Player.java
public class Player {
//----variables:
      public String username;
      
//----constructors (so no return type):
      public Player(){ username = "unknown"; }
      public Player(String nameSupplied) { username = nameSupplied; }

//----methods:
      public void greet() {
        System.out.println("hello " + username);
      }
}

our program executes from the main procedure:

//save as mainGame.java
public class mainGame {  
    public static void main(String[] args) { 
       Player robert = new Player("3l1t3_5n1p3r");
       robert.greet();
       
       Player sally = new Player();
       sally.greet();
       sally.username = "xX_memelord_Xx";
       sally.greet();
    }
}