What is inheritance in OOP?

The core idea

Inheritance lets a child class automatically get everything a parent class already has, and then add or change things. Instead of copying code, you extend it. A Dog is an Animal, so Dog can inherit eat and sleep from Animal and simply add bark.

class Animal {
public:
    void eat() { cout << "eating"; }
    void sleep() { cout << "sleeping"; }
};

class Dog : public Animal {   // Dog inherits from Animal
public:
    void bark() { cout << "woof"; }
};

Dog d;
d.eat();    // inherited
d.bark();   // its own

class Animal {
    void eat() { System.out.println("eating"); }
    void sleep() { System.out.println("sleeping"); }
}

class Dog extends Animal {   // Dog inherits from Animal
    void bark() { System.out.println("woof"); }
}

Dog d = new Dog();
d.eat();    // inherited
d.bark();   // its own

class Animal:
    def eat(self):
        print("eating")
    def sleep(self):
        print("sleeping")

class Dog(Animal):            # Dog inherits from Animal
    def bark(self):
        print("woof")

d = Dog()
d.eat()    # inherited
d.bark()   # its own

Common types of inheritance

• Single: one child inherits from one parent.
• Multilevel: a child inherits from a parent that itself inherits from another class.
• Hierarchical: many child classes inherit from one parent.
• Multiple: one class inherits from more than one class, which Java allows only through interfaces.

Why it helps

Inheritance removes duplicate code and creates a natural is a relationship. When shared logic lives in the parent, a fix or improvement there instantly benefits every child class.