Java Object-Oriented Programming Examples

This project contains Java examples demonstrating key object-oriented programming concepts including inheritance, polymorphism, method overriding, method overloading, and the use of super and this keywords.

Project Structure

Inheritance Examples

Animal Hierarchy

• Animal.java - Base class with atype field and aDes() method
• Dog.java - Extends Animal, demonstrates variable shadowing
• Cat.java - Extends Animal, demonstrates method overriding and overloading
• SuperThis.java - Demonstrates the use of super keyword
• ShadowOverride.java - Demonstrates variable shadowing and method overriding

Person/Student Hierarchy

• Person.java - Base class with personal information (SSN, name fields)
• Student.java - Extends Person, adds college class information
• StudentApp.java - Application demonstrating Student class usage

Banking System (Polymorphism Example)

• PolyBankAccount.java - Base bank account class
• PolySavingAccount.java - Extends PolyBankAccount, adds interest calculation
• PolyBankingApp.java - Demonstrates polymorphism with bank accounts

Class Composition vs Inheritance

• A.java - Simple class with hello() method
• B.java - Uses composition (has an A object)
• BB.java - Uses inheritance (extends A)
• AApp.java - Demonstrates composition approach
• BApp.java - Demonstrates inheritance approach

Key Concepts Demonstrated

1. Inheritance

• Classes extending other classes to inherit properties and methods
• Examples: Student extends Person, Dog extends Animal, PolySavingAccount extends PolyBankAccount

2. Polymorphism

• PolyBankingApp.java demonstrates runtime polymorphism where a PolyBankAccount reference can point to a PolySavingAccount object
• Method calls are resolved at runtime based on the actual object type

3. Method Overriding

• Subclasses override parent class methods (e.g., toString() in PolySavingAccount, aDes() in Dog and Cat)

4. Method Overloading

• Cat.java demonstrates method overloading with multiple aDes() methods having different parameters

5. Variable Shadowing

• Dog.java and Cat.java demonstrate how subclass variables can shadow parent class variables
• ShadowOverride.java shows the difference between variable shadowing and method overriding

6. Super and This Keywords

• SuperThis.java demonstrates using super to access parent class members
• Various classes show super() in constructors to call parent constructors

7. Composition vs Inheritance

• B.java shows composition (has-a relationship)
• BB.java shows inheritance (is-a relationship)
• Both approaches achieve similar functionality through different design patterns

Compilation and Execution

Compile All Java Files

javac *.java

Run Individual Applications

Animal Examples

java SuperThis
java ShadowOverride

Student Application

java StudentApp

Banking Application

java PolyBankingApp

Composition/Inheritance Examples

java AApp
java BApp

Notes

• Some files have .bak backup versions
• Compiled .class files are included in the project
• StudentApp.java uses JOptionPane for user input (requires GUI environment)
• PolyBankingApp.java calls a pay() method that may need to be implemented in PolyBankAccount or its subclasses

Learning Objectives

After reviewing this code, you should understand:

• How to create class hierarchies using inheritance
• The difference between method overriding and method overloading
• How polymorphism works in Java
• When to use composition vs inheritance
• How to use super and this keywords effectively
• The concept of variable shadowing in inheritance