🌟 Introduction

In this lab session, you will work with some of the most important concepts of Java:

• Inheritance
• Multilevel Inheritance
• Method Overriding
• Constructors in Inheritance

This session is designed to help you understand concepts through hands-on coding. By writing and running programs, you will learn how Java uses inheritance to build structured and reusable applications.

By the end of this lab, you will be able to:

✔ Create inheritance relationships
✔ Use multilevel inheritance
✔ Override methods
✔ Understand constructor execution flow

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⏱️ Lab Structure (2 Hours)

Time	Activity
0–15 min	Concept understanding
15–45 min	Single Inheritance Program
45–75 min	Multilevel Inheritance Program
75–100 min	Method Overriding
100–120 min	Constructors in Inheritance

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🧪 Part 1: Single Inheritance

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🎯 Program: Employee inherits Person

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💻 Code

class Person {

    String name;
    int age;

    void display() {
        System.out.println("Name: " + name);
        System.out.println("Age: " + age);
    }

}

class Employee extends Person {

    int empId;

    void showEmployeeId() {
        System.out.println("Employee ID: " + empId);
    }

}

public class Main {

    public static void main(String[] args) {

        Employee e = new Employee();

        e.name = "Ajay";
        e.age = 25;
        e.empId = 101;

        e.display();
        e.showEmployeeId();

    }

}

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🔎 Understanding the Program

• Person is the parent class
• Employee is the child class
• Employee inherits variables and methods from Person
• Object of Employee can access both parent and child members

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🧾 Output

Name: Ajay
Age: 25
Employee ID: 101

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🧠 Key Concept

👉 A child class can reuse properties of a parent class using extends.

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🔧 Practice

Modify the program by adding:

• salary in Employee
• Print salary along with other details

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🧪 Part 2: Multilevel Inheritance

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🎯 Program: Person → Employee → Manager

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💻 Code

class Person {

    String name;

    void showName() {
        System.out.println("Name: " + name);
    }

}

class Employee extends Person {

    int empId;

    void showEmployeeId() {
        System.out.println("Employee ID: " + empId);
    }

}

class Manager extends Employee {

    String department;

    void showDepartment() {
        System.out.println("Department: " + department);
    }

}

public class Main {

    public static void main(String[] args) {

        Manager m = new Manager();

        m.name = "Ajay";
        m.empId = 200;
        m.department = "IT";

        m.showName();
        m.showEmployeeId();
        m.showDepartment();

    }

}

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🔎 Understanding the Program

• Person → Base class
• Employee → inherits from Person
• Manager → inherits from Employee

👉 Manager gets access to:

• name
• empId
• department
• all methods

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🧾 Output

Name: Ajay
Employee ID: 200
Department: IT

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🧠 Key Concept

👉 Multilevel inheritance allows a class to inherit features from multiple levels of parent classes.

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🔧 Practice

Enhance the program by adding:

• salary in Employee
• bonus in Manager
• Display all values

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🧪 Part 3: Method Overriding

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🎯 Program: Salary Calculation

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💻 Code

class Employee {

    void calculateSalary() {
        System.out.println("Basic Salary");
    }

}

class Manager extends Employee {

    @Override
    void calculateSalary() {
        System.out.println("Manager Salary with Bonus");
    }

}

public class Main {

    public static void main(String[] args) {

        Employee e = new Manager();
        e.calculateSalary();

    }

}

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🔎 Understanding the Program

• calculateSalary() is defined in parent class
• Child class provides its own implementation
• This is called method overriding

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🧾 Output

Manager Salary with Bonus

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🧠 Key Concept

👉 Method call is decided at runtime, not compile time.

This is called:

👉 Runtime Polymorphism

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🔧 Practice

Create a new class:

• Intern
• Override calculateSalary() with different output

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🧪 Part 4: Constructors in Inheritance

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🎯 Program: Constructor Chaining

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💻 Code

class Person {

    Person() {
        System.out.println("Person Constructor");
    }

}

class Employee extends Person {

    Employee() {
        System.out.println("Employee Constructor");
    }

}

class Manager extends Employee {

    Manager() {
        System.out.println("Manager Constructor");
    }

}

public class Main {

    public static void main(String[] args) {

        Manager m = new Manager();

    }

}

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🔎 Understanding the Program

When object is created:

Manager m = new Manager();

Execution order:

Person → Employee → Manager

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🧾 Output

Person Constructor
Employee Constructor
Manager Constructor

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🧠 Key Concept

👉 Constructors execute from parent to child

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🔧 Practice

Modify the program:

• Add parameterized constructor
• Use super()

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🎯 Final Combined Practice

Create a program with:

• Person → Employee → Manager
• Constructor chaining
• Method overriding

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🧠 Key Takeaways

✔ Inheritance helps in code reuse
✔ Multilevel inheritance builds hierarchy
✔ Method overriding enables dynamic behavior
✔ Constructors execute in chain (parent → child)
✔ Runtime polymorphism decides method execution

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🏁 Conclusion

This lab session provided hands-on experience with core inheritance concepts in Java. By implementing these programs, you now understand how classes are connected, how behavior can be modified, and how objects are initialized.

These concepts form the foundation of object-oriented programming and are essential for:

• Writing efficient Java programs
• Building real-world applications
• Preparing for technical interviews