Inheritance in Java

🎯 Goal of Inheritance

Inheritance enables code reuse and creates a hierarchical relationship between classes.

It allows a subclass to inherit fields and methods from a superclass and also define its own behavior.

🏢 Real-World Scenario: Employee Management System

Consider a company with:

• Common attributes for all employees (name, ID, salary)

• Specific behaviors or fields for different roles:

  • Manager has a team size

  • Engineer has a specialization

  • Intern has a duration

This is a perfect use case for inheritance.

🔹 Java Code Example

1️⃣ Superclass: Employee public class Employee {

protected String name;

protected int employeeId;

protected double salary;

public Employee(String name, int employeeId, double salary) {

this.name = name;

this.employeeId = employeeId;

this.salary = salary;

}

public void displayDetails() {

System.out.println("Name: " + name);

System.out.println("ID: " + employeeId);

System.out.println("Salary: ₹" + salary);

}

} 2️⃣ Subclass: Manager public class Manager extends Employee {

private int teamSize;

public Manager(String name, int employeeId, double salary, int teamSize) {

super(name, employeeId, salary); // 🪜 Call to parent constructor

this.teamSize = teamSize;

}

@Override

public void displayDetails() {

super.displayDetails(); // Reuse base info

System.out.println("Team Size: " + teamSize);

}

} 3️⃣ Subclass: Engineer public class Engineer extends Employee {

private String specialization;

public Engineer(String name, int employeeId, double salary, String specialization) {

super(name, employeeId, salary);

this.specialization = specialization;

}

@Override

public void displayDetails() {

super.displayDetails();

System.out.println("Specialization: " + specialization);

}

} 4️⃣ Subclass: Intern public class Intern extends Employee {

private int internshipDurationMonths;

public Intern(String name, int employeeId, double salary, int duration) {

super(name, employeeId, salary);

this.internshipDurationMonths = duration;

}

@Override

public void displayDetails() {

super.displayDetails();

System.out.println("Internship Duration: " + internshipDurationMonths + " months");

}

} 🔄 Usage in Main public class Main {

public static void main(String[] args) {

Manager m = new Manager("Alice", 1001, 90000.0, 5);

Engineer e = new Engineer("Bob", 1002, 75000.0, "Backend");

Intern i = new Intern("Charlie", 1003, 15000.0, 6);

m.displayDetails();

System.out.println("------------------");

e.displayDetails();

System.out.println("------------------");

i.displayDetails();

}

} 🧠 Key Concepts Demonstrated

Concept	Description
super()	Calls constructor of the parent class
@Override	Redefines inherited method to add subclass-specific behavior
protected fields	Allow access in subclasses
Code reuse	All subclasses reuse name, salary, and displayDetails() from Employee

💬 Interview-Ready Explanation

"In my employee management model, I used inheritance to avoid repeating common attributes and behavior. I created a superclass Employee and extended it with subclasses like Manager and Engineer. Each subclass overrides displayDetails() to show role-specific data, demonstrating polymorphism as well."

🧪 Student Practice Challenge

Create a class Vehicle with properties like make, model, price.Then extend it to create:

• ElectricCar (with battery capacity),

• Bike (with gear count),

• Truck (with payload limit).

Override a method displayInfo() to include subclass details.