Notes

• it is a class in java that can’t be instantiated but is used as a blueprint for other classes. it is designed to be extended by subclasses.
• it is declared using keyword abstract.
• it may contain
  • abstract methods - methods without a body, must be implemented by subclass
  • concrete methods - methods with implementation that subclasses use or override.
  • fields - constructors and nested classes.
• cannot be instantiated.
• purpose -
  • provide a common structure and behavior for related classes.
  • enforces a contract by requiring subclasses to implement abstract methods.
  • enables code reuse through shared fields and methods.
  • support polymorphism by allowing abstract class references to point to subclass objects.

abstract class Animal {
    String name;

    // Constructor
    Animal(String name) {
        this.name = name;
    }

    // Abstract method (must be implemented by subclasses)
    abstract void makeSound();

    // Concrete method (shared by all subclasses)
    void sleep() {
        System.out.println(name + " is sleeping.");
    }
}

class Dog extends Animal {
    Dog(String name) {
        super(name); // Call superclass constructor
    }

    @Override
    void makeSound() {
        System.out.println(name + " says Woof!");
    }
}

class Cat extends Animal {
    Cat(String name) {
        super(name);
    }

    @Override
    void makeSound() {
        System.out.println(name + " says Meow!");
    }
}

class Main {
    public static void main(String[] args) {
        // Animal animal = new Animal("Generic"); // Error: Cannot instantiate
        Animal dog = new Dog("Buddy");
        Animal cat = new Cat("Whiskers");

        dog.makeSound(); // Output: Buddy says Woof!
        dog.sleep();     // Output: Buddy is sleeping.
        cat.makeSound(); // Output: Whiskers says Meow!
        cat.sleep();     // Output: Whiskers is sleeping.
    }
}