Switch from Kotlin Developer to Java Developer

A step-by-step plan for Kotlin developers to become skilled Java developers. Learn Java basics, explore its ecosystem, and build a real-world project.

Weekly Hours: 10
Estimated Weeks: 8

Phases

Java Language Foundations

Build strong Java basics. Focus on syntax, object-oriented concepts, and essential Java libraries. Practice by converting Kotlin code to Java.

2 weeks

Understand Java syntax and structure
Use classes, objects, and methods in Java
Write simple Java programs
Convert simple Kotlin code to Java

Write Java classes (Person.java)
Use basic data structures (ArrayList)
Handle exceptions (try-catch)
Convert Kotlin functions to Java

Official Java Tutorials
Java for Beginners Book
Online Practice Platform
Java Documentation

Submit 3 Java programs with documentation
Convert 2 Kotlin snippets to Java and explain changes

Java Ecosystem & Tools

Get familiar with Java tools like build systems and IDEs. Learn about dependency management and Java project layouts. Practice using these tools.

2 weeks

Set up Java using a popular IDE
Use a Java build tool (Gradle or Maven)
Manage project dependencies
Understand Java directory structure

Create Java project (IntelliJ, Eclipse)
Write build scripts (Gradle build.gradle)
Add library dependencies (JUnit, Gson)
Navigate project folders

Java IDE Guide
Gradle/Maven User Guide
Sample Java Project Repositories
Java Library Index

Set up a working Java project with a build tool
Include at least 2 library dependencies

Spring Boot Web Project

Build a practical web application using Spring Boot. Learn to set up routing, handle forms, manage state, run tests, and deploy your app.

3 weeks

Use Spring Boot to create a web server
Implement routing and request handling
Build and process web forms
Test Java code and web endpoints
Deploy a Java app

Build endpoints (Spring Boot Controller)
Handle form input (Spring Model/DTO classes)
Manage state (in-memory storage)
Write unit and integration tests (JUnit)
Deploy to cloud platform (Heroku)

Spring Boot Getting Started Guide
JUnit Official Docs
Heroku Java Deployment Guide
Sample Spring Boot Projects

Deploy a Spring Boot web app demo
Write 5 passing unit tests (JUnit)
Add user input validation on forms
Show CI badge from GitHub Actions

Showcase & Application

Prepare your project for review. Write documentation and a professional README. Practice walkthrough and code demonstrations.

1 weeks

Write project documentation
Show project features and code
Get feedback and improve project
Practice interview questions

Write clear README.md (project overview, setup, usage)
Explain code choices (comments, presentation)
Summarize learning in documentation
Demo project locally or via video

Java README Examples
Tech Interview Sample Questions
Peer Feedback Groups

Publish project with README and setup guide
Deliver a 5-minute project walkthrough

Weekly Plan

Week	Focus	Why	Tasks	Deliverables
1	Java basics and syntax	Strong fundamentals make learning advanced Java easier.	Read Java basics (Official Java Tutorials), Write simple Java programs (HelloWorld, Calculator), Convert basic Kotlin functions to Java, Submit code samples for review	3 Java program files, 2 converted Kotlin-to-Java files
2	Object-oriented Java and exceptions	Java uses object-oriented style in most projects.	Define classes and objects (Person.java, Animal.java), Implement inheritance and interfaces, Write code using Java Collections (ArrayList, HashMap), Handle exceptions with try-catch blocks	2 Java class files, Code using collections and exceptions
3	Java tools: IDE, build, dependencies	Every real Java project uses these tools.	Install and set up IDE (IntelliJ/Eclipse), Create a Java project, Add dependencies (JUnit, Gson) using Gradle or Maven, Explore folder structure	Java project with build file, Project including 2 libraries
4	Spring Boot introduction and setup	Spring Boot is common for building Java web apps.	Read Spring Boot basics (Getting Started Guide), Create a new Spring Boot web project, Set up first endpoint (GET /hello), Run and test locally	Running Spring Boot starter project, Accessible /hello endpoint
5	Building routes and processing forms	Interactive web apps need routing and forms.	Build multiple endpoints (GET/POST), Create web form for user input (e.g., /register), Handle form data in Java (DTO class), Validate and respond to user input	Routes for listing and adding users, Input-validated web form
6	App state and testing	Manage data and write reliable, testable code.	Implement in-memory data storage (user list), Write unit tests using JUnit, Test endpoints with integration tests, Fix failing tests and refactor code	3 unit tests, Store and retrieve users in memory
7	Deployment and automation	Deployment shows real-world skills and app readiness.	Prepare app for deployment (Heroku/Cloud docs), Set up continuous integration (GitHub Actions), Deploy app online, Show badge for passing builds	Live demo link, CI badge on README
8	Documentation, review, and interview practice	Good docs and communication impress employers.	Write and format detailed README (setup, usage, features), Record or demo the project, Ask for feedback from a peer, Practice explaining your project	Published README, Project walkthrough video or demo

Daily Plan

Monday

Read one guide or tutorial
Write 1-2 small code examples

Tuesday

Implement a feature or class
Test and debug code

Wednesday

Work on current week's project tasks
Write documentation for what you completed

Thursday

Add a new skill (library, tool, form, or test)
Try a related coding exercise

Friday

Review the week's progress
Share code for feedback
Plan next week's tasks