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bala d kaveri

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🚀 Day 9 of My Java Automation Journey – Types of Inheritance

#java #inheritance #basic #javascript

On Day 9, I learned about:

✅ Different Types of Inheritance in Java

Yesterday we discussed Single Inheritance.
Today I explored all inheritance types and understood how Java handles them internally.

📌 What is Inheritance?

Inheritance is a mechanism where:

A child class acquires the properties and behaviors of a parent class.

It represents an:

🔁 IS-A Relationship

Example:

Developer is an Employee

Senior_Dev is a Developer

📚 Types of Inheritance in Java

1️⃣ Single Inheritance
2️⃣ Multiple Inheritance
3️⃣ Hierarchical Inheritance
4️⃣ Multilevel Inheritance
5️⃣ Hybrid Inheritance

Let’s understand each one clearly 👇

1️⃣ Single Inheritance
📖 Definition

When one child class inherits from one parent class.

Structure:

Parent → Child
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Example:
Employee → Developer
2️⃣ Multiple Inheritance
📖 Definition

When one child class tries to inherit from more than one parent class.

Structure (Not allowed in Java classes):

Mom
   ↘
    Child
   ↗
Dad
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❌ Problem: Ambiguity Issue

If both parent classes have the same method:

void work()

Then Java cannot decide:

Which parent's method should the child use?

This is called:

⚠ Ambiguity Problem

🚫 Important

Java does NOT support multiple inheritance using classes.

But…

✅ It supports multiple inheritance via Interfaces (we will learn later).
If we try:

class Child extends Mom, Dad

👉 It throws a compile-time error.

3️⃣ Hierarchical Inheritance
📖 Definition

When multiple child classes inherit from the same parent class.

Structure:

        Employee
        /      \
   Developer   Testing
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Example:

Developer extends Employee

Testing extends Employee

Both share common properties like:

salary
empId
common methods

This improves reusability.

4️⃣ Multilevel Inheritance (Important Today)
📖 Definition

When a class inherits from another class, and then another class inherits from that class.

Structure:

Grandparent → Parent → Child
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Example:

Employee → Developer → Senior_Dev
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This is called Multilevel Inheritance.

💻 Now Let’s Understand the Code
🔹 Step 1: Employee (Parent Class)

public class Employee {
    int salary;

    void Welcome() {
        System.out.println("Welcome");
    }
}
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🔍 Explanation

salary → Instance variable

Welcome() → Method
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Acts as base class

Contains common properties

🔹 Step 2: Developer (Child of Employee)
p

ublic class Developer extends Employee {

    String Designation = "Devloper";

    void Welcome() {
        System.out.println("Welcome 2");
    }
}
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🔍 What is happening here?

Developer extends Employee
Inherits salary
Inherits Welcome() method
Adds new variable:
Designation
Overrides Welcome() method

👉 This is called Method Overriding (next topic 😉)

🔹 Step 3: Senior_Dev (Child of Developer)

public class Senior_Dev extends Developer
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Now the inheritance chain becomes:

Employee
   ↓
Developer
   ↓
Senior_Dev
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🔎 Execution Flow of Senior_Dev

Senior_Dev Senior1 = new Senior_Dev();
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What happens in memory?

The object contains:

salary (from Employee)
Designation (from Developer)
Welcome() (overridden version from Developer)
Senior_Dev part

Code Execution

Senior1.Welcome();
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Calls Developer’s Welcome() method

Output:

Welcome 2
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Because method overriding happens.

Senior1.Designation = "Senior Developer";
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Changes inherited variable from Developer

Senior1.salary = 10000;
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  • Accessing Employee variable
  • Even though it's 2 levels above

Final Output:

Welcome 2
Senior Developer
Salary 10000
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🎯 Why Multilevel Inheritance is Powerful

✅ Reusability across multiple layers
✅ Real-world modeling
✅ Code organization
✅ Easy expansion

Real-world example:

Person → Employee → Developer → Senior Developer
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5️⃣ Hybrid Inheritance
📖 Definition

Combination of two or more types of inheritance.

Example:

  • Hierarchical + Multilevel

⚠ Java does not support Hybrid inheritance using classes directly (because it may involve multiple inheritance).

But it can be achieved using interfaces.

🧠 Important Concepts Learned Today

✔ Types of inheritance
✔ Why multiple inheritance is not supported
✔ Ambiguity problem
✔ Hierarchical inheritance structure
✔ Multilevel inheritance
✔ Method overriding preview
✔ Real-world class hierarchy

🏁 Day 9 Key Takeaways

Java supports:

Single
Multilevel
Hierarchical

Java does NOT support:

Multiple inheritance (with classes)
Java supports multiple inheritance:
Via Interfaces only

👨‍🏫 Trainer: Nantha from Payilagam

🤖 A Small Note
I used ChatGPT to help structure and refine this blog while ensuring the concepts remain aligned with my trainer’s explanations.

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