Access Modifiers: Public, Private, Protected

Public: can be accessed from anywhere inside the program, that is, they can be accessed within the same class as well as from outside the different classes
Private: they can be accessed only within the same class where they have been declared, they will not be visible to the outside world
Protected: used to access the methods or data members of a class within the same package as well as outside the package but only through inheritance
- more visibility than private, less than public

public class Cow {

    // instance variables
    private String cowType;
    private String sound;
    protected int numMilkings;

    public Cow (String cowType, String sound){
        this.numMilkings = 0;
        this.cowType = cowType;
        this.sound = sound;
    }

    public int getNumMilkings(){
        return numMilkings;
    }

    public void setSound(String sound){
        this.sound = sound;
    }

    public String toString(){
        return "Type of Cow: " + cowType + "; " + "Sound: " + sound + "; " + "Number of Milkings: " + numMilkings;
    }

    public static void main(String[] args) {
        Cow firstCow = new Cow("holstein", "moo");
        System.out.println(firstCow);
        System.out.println("Number of Milkings: " + firstCow.getNumMilkings());
        firstCow.setSound("oink!");
        System.out.println("Mutated Cow:" + firstCow);
    }
}

Cow.main(null);

Subclasses

Method to create hierarchy between classes by inheriting from other classes
parent and child classes
extends extend a class to show its inherited and extends functionality
Subclass inherits all methods and fields from superclass, and constructor can be carried out from subclass
super refers to superclass or parent objects

// Hacks 1
private class Plane {
    private String model = "Boeing 737";
    private int age = 3; //two attributes

    public void getAge(String model, int age) {
        println("Age: " + age);
    }
}

private class Jet extends Plane {
    private String color = "blue";
    
}

Overload & Override

Overload happens when there are two methods with same name but different arguments or parameters
Method override happens when child class has the same method that is present in a parent class, overwrites base class method

//hack 2
public class Plane {
    private String model = "Boeing 737";
    private int age = 3;

    public void engineBurr() {
        System.out.println("brrrrrr");
    }
}

private class Jettison extends Plane {
    public Jettison(String model, int age, String color) {
        super(model, age); 
        this.color = color; 

        @Override
        public void engineBurr() {
        System.out.println("BRRRRRRRRR"); 
    }

}

Polymorphism

Ability of class to provide different implementations of methods, such as overloading, overriding, late binding

//Hack 3
private class Jets extends Plane {
    @Override
    public void getAge(String model, int age, String color) {
        println("Age: " + age);
    }

    public void getAge(int age, String color) {
        println("Age: " + age);
    }
}