Inheritance in Java

// PARENT CLASS (Superclass)
class Animal {
    String name;
    int age;
    public Animal(String name, int age) {
        this.name = name;
        this.age = age;
    }
    public void eat() {
        System.out.println(name + " is eating");
    }
    public void sleep() {
        System.out.println(name + " is sleeping");
    }
}
// CHILD CLASS (Subclass) - inherits from Animal
class Dog extends Animal {
    String breed;
    public Dog(String name, int age, String breed) {
        super(name, age);  // Call parent constructor
        this.breed = breed;
    }
    // Dog has all Animal methods PLUS its own methods
    public void bark() {
        System.out.println(name + " says: Woof! Woof!");
    }
}
// Using inheritance
class InheritanceDemo {
    public static void main(String[] args) {
        Dog myDog = new Dog("Buddy", 3, "Golden Retriever");
        // Dog can use Animal methods (inherited)
        myDog.eat();      // From Animal class
        myDog.sleep();    // From Animal class
        // Dog can use its own methods
        myDog.bark();     // From Dog class
        System.out.println("Name: " + myDog.name);  // Inherited field
        System.out.println("Breed: " + myDog.breed); // Own field
    }
}

class Vehicle {
    String brand;
    int speed;
    public Vehicle(String brand) {
        this.brand = brand;
        this.speed = 0;
    }
    // Parent method
    public void start() {
        System.out.println("Vehicle is starting...");
    }
    public void displayInfo() {
        System.out.println("Brand: " + brand);
        System.out.println("Speed: " + speed + " km/h");
    }
}
class Car extends Vehicle {
    int numberOfDoors;
    public Car(String brand, int doors) {
        super(brand);  // Call parent constructor
        this.numberOfDoors = doors;
    }
    // OVERRIDE parent method - provide own version
    @Override
    public void start() {
        System.out.println("Car engine starting... Vroom!");
        super.start();  // Can still call parent version if needed
    }
    // Child can have its own methods too
    public void honk() {
        System.out.println("Beep beep!");
    }
}
class Motorcycle extends Vehicle {
    boolean hasSidecar;
    public Motorcycle(String brand, boolean sidecar) {
        super(brand);
        this.hasSidecar = sidecar;
    }
    // OVERRIDE - Motorcycle starts differently than Car
    @Override
    public void start() {
        System.out.println("Motorcycle engine revving... Brrrm!");
    }
}
class OverrideDemo {
    public static void main(String[] args) {
        Car myCar = new Car("Toyota", 4);
        Motorcycle myBike = new Motorcycle("Harley", false);
        // Each calls its own overridden version!
        myCar.start();      // "Car engine starting... Vroom!"
        myBike.start();     // "Motorcycle engine revving... Brrrm!"
        myCar.honk();       // Car's own method
    }
}

class Person {
    String name;
    int age;
    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
    public void introduce() {
        System.out.println("Hi, I'm " + name);
    }
}
class Student extends Person {
    String studentId;
    double gpa;
    public Student(String name, int age, String id, double gpa) {
        // MUST call parent constructor first!
        super(name, age);  // Calls Person constructor
        this.studentId = id;
        this.gpa = gpa;
    }
    @Override
    public void introduce() {
        // Call parent's introduce first
        super.introduce();
        // Add student-specific information
        System.out.println("I'm a student with ID: " + studentId);
        System.out.println("My GPA is: " + gpa);
    }
    public void study() {
        System.out.println(name + " is studying");  // Can access parent's fields
    }
}
class SuperDemo {
    public static void main(String[] args) {
        Student alice = new Student("Alice", 20, "S12345", 3.8);
        alice.introduce();
        // Output:
        // Hi, I'm Alice                    (from parent)
        // I'm a student with ID: S12345    (from child)
        // My GPA is: 3.8                   (from child)
        alice.study();
    }
}

// SINGLE INHERITANCE
class Animal {
    void eat() { System.out.println("Eating..."); }
}
class Dog extends Animal {
    void bark() { System.out.println("Barking..."); }
}
// MULTILEVEL INHERITANCE
class Puppy extends Dog {
    void play() { System.out.println("Playing..."); }
}
// HIERARCHICAL INHERITANCE
class Cat extends Animal {
    void meow() { System.out.println("Meowing..."); }
}
class Bird extends Animal {
    void fly() { System.out.println("Flying..."); }
}
class TypesDemo {
    public static void main(String[] args) {
        // Single: Dog inherits from Animal
        Dog dog = new Dog();
        dog.eat();   // From Animal
        dog.bark();  // Own method
        // Multilevel: Puppy inherits from Dog, Dog inherits from Animal
        Puppy puppy = new Puppy();
        puppy.eat();   // From Animal (grandparent)
        puppy.bark();  // From Dog (parent)
        puppy.play();  // Own method
        // Hierarchical: Cat and Bird both inherit from Animal
        Cat cat = new Cat();
        cat.eat();   // From Animal
        cat.meow();  // Own method
        Bird bird = new Bird();
        bird.eat();  // From Animal
        bird.fly();  // Own method
    }
}

// Base class for all employees
class Employee {
    protected String name;
    protected String employeeId;
    protected double baseSalary;
    public Employee(String name, String id, double salary) {
        this.name = name;
        this.employeeId = id;
        this.baseSalary = salary;
    }
    public void work() {
        System.out.println(name + " is working");
    }
    public double calculateSalary() {
        return baseSalary;
    }
    public void displayInfo() {
        System.out.println("Name: " + name);
        System.out.println("ID: " + employeeId);
        System.out.println("Salary: $" + calculateSalary());
    }
}
// Specialized employee types
class Developer extends Employee {
    private String programmingLanguage;
    private int projectsCompleted;
    public Developer(String name, String id, double salary, String language) {
        super(name, id, salary);
        this.programmingLanguage = language;
        this.projectsCompleted = 0;
    }
    @Override
    public void work() {
        System.out.println(name + " is coding in " + programmingLanguage);
    }
    public void completeProject() {
        projectsCompleted++;
        System.out.println("Project completed! Total: " + projectsCompleted);
    }
    @Override
    public double calculateSalary() {
        // Developers get bonus for each project
        return baseSalary + (projectsCompleted * 1000);
    }
}
class Manager extends Employee {
    private int teamSize;
    private double bonus;
    public Manager(String name, String id, double salary, int teamSize) {
        super(name, id, salary);
        this.teamSize = teamSize;
        this.bonus = 0;
    }
    @Override
    public void work() {
        System.out.println(name + " is managing a team of " + teamSize);
    }
    public void giveBonus(double amount) {
        this.bonus = amount;
    }
    @Override
    public double calculateSalary() {
        // Managers get base salary plus bonus
        return baseSalary + bonus;
    }
}
class EmployeeDemo {
    public static void main(String[] args) {
        Developer dev = new Developer("Alice", "DEV001", 80000, "Java");
        Manager mgr = new Manager("Bob", "MGR001", 100000, 5);
        // Each works differently
        dev.work();        // "Alice is coding in Java"
        mgr.work();        // "Bob is managing a team of 5"
        // Update their stats
        dev.completeProject();
        dev.completeProject();
        mgr.giveBonus(15000);
        // Display info with calculated salaries
        System.out.println("\n--- Developer Info ---");
        dev.displayInfo();  // Salary includes project bonuses
        System.out.println("\n--- Manager Info ---");
        mgr.displayInfo();  // Salary includes bonus
    }
}