Inheritance in Java

#java #programming #tutorial #beginners

What is Inheritance?

Inheritance in Java is a feature where one class (child) can use the properties and methods of another class (parent).

The class that is inherited from is called Parent / Superclass
The class that inherits is called Child / Subclass
Java uses the keyword extends to achieve inheritance.

In short

Parent class → Superclass
Child class → Subclass
Keyword used → extends

🧠 Real-World Idea

Think like this

A Car is a Vehicle
A Dog is an Animal
A Student is a Person

This “IS-A” relationship is exactly what inheritance represents.

💻 Simple Code Example

class Vehicle {
    void start() {
        System.out.println("Vehicle is starting");
    }
}

class Car extends Vehicle {
    void drive() {
        System.out.println("Car is driving");
    }

    public static void main(String[] args) {
        Car c = new Car();
        c.start();   // inherited
        c.drive();   // own method
    }
}

📌 Why Do We Need Inheritance?

Code reusability
Reduces duplicate code
Improves maintainability
Supports method overriding
Helps achieve runtime polymorphism

📌 Types of Inheritance

1️⃣ Single Inheritance

One child → One parent

class A {}
class B extends A {}

2️⃣ Multilevel Inheritance

Grandparent → Parent → Child

class A {}
class B extends A {}
class C extends B {}

Example:

class Vehicle {
    void start() {
        System.out.println("Vehicle is starting");
    }
}

class Car extends Vehicle {
    void wheels() {
        System.out.println("Car has 4 wheels");
    }
}

class Tesla extends Car {
    void autopilot() {
        System.out.println("Tesla has autopilot feature");
    }
}

public class Main {
    public static void main(String[] args) {
        Tesla t = new Tesla();

        t.start();       // From Vehicle
        t.wheels();      // From Car
        t.autopilot();   // From Tesla
    }
}

3️⃣ Hierarchical Inheritance

One parent → Multiple children

class A {}
class B extends A {}
class C extends A {}

Example:

class Bank {
    void deposit() {
        System.out.println("Money deposited");
    }

    void withdraw() {
        System.out.println("Money withdrawn");
    }
}

class SavingsAccount extends Bank {
    void interest() {
        System.out.println("Savings Account earns interest");
    }
}

class CurrentAccount extends Bank {
    void overdraft() {
        System.out.println("Current Account has overdraft facility");
    }
}

public class Main {
    public static void main(String[] args) {

        SavingsAccount s = new SavingsAccount();
        s.deposit();      // From Bank
        s.interest();     // From SavingsAccount

        CurrentAccount c = new CurrentAccount();
        c.withdraw();     // From Bank
        c.overdraft();    // From CurrentAccount
    }
}

4️⃣ Multiple Inheritance

Java does NOT allow this with classes because of ambiguity (Diamond Problem).

✅ Java supports multiple inheritance using interfaces.

✅ Advantages of Inheritance