Access Modifier

Package meant folder in java.

Subclass meant all classes implement from parent or super class.

Classes & Objects

• Class → a blueprint (it defines what properties and behaviors something has).
• Object → an instance of that class (a concrete thing created from the blueprint).

class Car {
    private String model;
    private int year;

    // Custom Constructor this will override the default one.
    Car(String model, int year) {
        this.model = model;
        this.year = year;
    }

    public String getModel() {
        return model;
    }

    public void setModel(String model) {
        this.model = model;
    }

    public int getYear() {
        return year;
    }

    public void setYear(int year) {
        this.year = year;
    }
}

Encapsulation

• Definition: Wrapping fields and methods into a single unit (the class) and restricting direct access to fields.
• Achieved with private fields + public getters/setters.
• Benefits: data hiding, controlled access, validation, maintainability.

class BankAccount {
    private double balance; 
    // hidden from outside
		// balance is like a private state vault.
		// If balance were public, any external code could bypass the rules, and the        n the logic of the whole class (getBalance, deposit, withdraw) would be unreliable.
		// With encapsulation it will makes sure all updates happen safely and consistently.
		
    public double getBalance() {
        return balance;
    }

    public void deposit(double amount) {
        if (amount > 0) balance += amount;
    }

    public void withdraw(double amount) {
        if (amount > 0 && amount <= balance) balance -= amount;
    }
}

2. Inheritance

• Definition: A class (child/subclass) can inherit properties & behaviors from another class (parent/superclass).
• Promotes code reuse.
• Keyword: extends.

class Animal {
    void eat() {
        System.out.println("This animal eats food");
    }
}

class Dog extends Animal {
    void bark() {
        System.out.println("Woof!");
    }
}

public class Main {
    public static void main(String[] args) {
        Dog d = new Dog();
        d.eat();   // inherited from Animal
        d.bark();  // defined in Dog
    }
}