Java Interview Preparation Course

In this section, you will:

• Create a sample Java project using IntelliJ IDEA.

• Understand the basic structure of a Java program, including package, class, and main method.

• Learn about Java syntax rules and how to write a clean, error-free Java program.

• Explore the four types of access modifiers in Java:

  • private

  • default

  • protected

  • public

• Understand where and how to use each access modifier with clear examples.

In this section, you will:

• Learn the difference between primitive and non-primitive data types in Java.

• Understand the syntax and usage of key primitive data types such as:

  • float

  • char

  • boolean

• Explore non-primitive data types with a focus on:

  • Declaring and initializing arrays

  • Printing array values using a for loop

• Practice these concepts within a real-time Java project setup, helping you prepare for both interviews and real-world development.

In this section, we will explore MySQL by working with a real-time example — the Bank Customer table. You'll learn how to create and manage your database using SQL commands, categorized into:

1. DDL (Data Definition Language) – Create, alter, and drop tables.

2. DML (Data Manipulation Language) – Insert, update, and delete records.

3. DQL (Data Query Language) – Retrieve data using SELECT queries.

4. DCL (Data Control Language) – Grant and revoke access to users.

5. TCL (Transaction Control Language) – Manage transactions using COMMIT, ROLLBACK, and SAVEPOINT.

Each concept will be explained with practical, real-time queries and examples based on the Bank Customer Management System to help you gain hands-on experience.

In this section, we’ll lay the foundation for our project by understanding key backend technologies and concepts used in real-world Java development.

Here’s what you’ll learn:

• What is Spring Boot ?

• What are Microservices?.

• Microservices Architecture Diagram

• What is a REST AP?

• What is Hibernate & JPA?

• What is MySQL?

• Microservice Folder Structure

By the end of this section, you'll clearly understand the tools and architecture we’ll use to build our Bank Customer Management System using Spring Boot and Microservices.

In this section, we will set up our Java Spring Boot project using Spring Initializr (start.spring.io).
You'll learn how to configure the basic project structure by selecting the correct Group ID, Artifact ID, and essential dependencies required for building our Customer Microservice.

We will cover:

• How to use Spring Initializr to bootstrap a new project.

• Choosing the right dependencies like Spring Web, Spring Data JPA, MySQL Driver, etc.

• Downloading and importing the project into an IDE (such as IntelliJ or Eclipse).

• Understanding the initial folder structure and configurations.

By the end of this section, you'll have a fully set up Spring Boot project ready for developing the Customer Microservice!

In this section, we’ll start building the core of our Bank Customer Management System by creating the Customer Microservice using Spring Boot.

Here’s what we’ll cover:

• Configuring the application.properties file for database connection and server port.

In this section, we’ll dive deep into Object-Oriented Programming (OOPs) Encapsulation concept and learn how to apply them using real-world examples from our Bank Customer Management System project

1. Creating the Customer Entity mapped to the MySQL customer table.

2. Using private variables and public getter/setter methods to protect data and control access.

3. Validating inputs like email format and password length using simple rules.

In this section, we’ll dive deep into Object-Oriented Programming (OOPs) Encapsulation concept and learn how to apply them using real-world examples from our Bank Customer Management System project

1. Creating CustomerService as an interface or abstract class.

2. Hiding internal logic while exposing only essential operations like registerCustomer() and getCustomerById().

3. Implementing the abstraction in CustomerServiceImpl.

1. Compile-Time Polymorphism:
   Method Overloading in CustomerServiceImpl – multiple getById() methods with different parameters.

2. Run-Time Polymorphism:
   Method Overriding from CustomerService to CustomerServiceImpl – demonstrating dynamic method dispatch and behavior change during execution.

1. Single Inheritance: CustomerServiceImpl extends CustomerService.

2. Hierarchical Inheritance: Multiple service classes like CustomerServiceImpl and AddressServiceImpl implementing the same interface.

3. Multilevel Inheritance: Adding intermediate abstract/service layers.

4. Multiple Inheritance (via interfaces): Implementing CustomerService and BankService in one class.

5. Hybrid Inheritance: A real-world mix of inheritance types using interfaces and abstract classes.

6. Usage of @Qualifier annotation to resolve multiple bean injection conflict

What You'll Learn in This Section:

• How to create a Spring Boot controller for handling customer-related operations

• Understanding the role of @RestController, @RequestMapping, and @PostMapping

• Creating the Register Customer API using @RequestBody and service injection

• Creating the Get Customer by ID API using @PathVariable

• Setting up the CustomerRepository interface using Spring Data JPA

• How JpaRepository handles basic CRUD operations without writing boilerplate code

• Writing business logic in CustomerServiceImpl for saving and retrieving customer data

• Testing the REST APIs using Postman with real JSON requests

• Explaining the flow between Controller → Service → Repository → Database

• Building and validating your first working Customer Microservice API endpoints

1. Quickly revise all core Java basics in one place.

2. Strengthen their understanding of key concepts like data types, control flow, OOP basics, and syntax.

3. Use the cheat sheet for last-minute interview preparation.

4. Build more confidence in foundational Java topics before facing technical rounds.

5. Save time by referring to this consolidated resource instead of browsing multiple sources.