Docker or Java First: What Beginners Should Pick

// Greeting.java - compile: javac Greeting.java   run: java Greeting
import java.util.List;

public class Greeting {

    record Course(String name, int weeks) {}

    public static void main(String[] args) {
        List<Course> courses = List.of(
            new Course("Java Basics", 6),
            new Course("Spring Boot", 8),
            new Course("Docker", 3)
        );

        int total = 0;
        for (Course c : courses) {
            System.out.println(c.name() + " -> " + c.weeks() + " weeks");
            total += c.weeks();
        }
        System.out.println("Total plan: " + total + " weeks");
    }
}

# Dockerfile - packages Greeting.java into a container
FROM eclipse-temurin:21-jdk
WORKDIR /app
COPY Greeting.java .
RUN javac Greeting.java
CMD ["java", "Greeting"]

# Build and run (Docker must be installed):
#   docker build -t greeting-app .
#   docker run --rm greeting-app

Java developer roadmap (Docker added at the right time)

Stage 1  Java syntax, conditions, loops, methods
Stage 2  OOP: classes, objects, inheritance, interfaces
Stage 3  Collections, exceptions, file handling
Stage 4  SQL and JDBC basics
Stage 5  Spring Boot REST API
Stage 6  Docker: containerise your Spring Boot app
Stage 7  Git, testing (JUnit), deployment basics

DevOps roadmap (some coding still required)

Stage 1  Linux command line and file system
Stage 2  Bash scripting basics
Stage 3  One language basics (Python or Java)
Stage 4  Git and GitHub
Stage 5  Docker: images, containers, volumes, compose
Stage 6  CI/CD pipelines
Stage 7  Cloud basics and Kubernetes introduction

# Everyday Docker commands for beginners
docker --version                 # check installation
docker pull nginx                # download an image
docker run -d -p 8080:80 nginx   # run it, open http://localhost:8080
docker ps                        # list running containers
docker logs <container_id>       # view logs
docker stop <container_id>       # stop a container
docker images                    # list images
docker rm <container_id>         # remove a stopped container

# docker-compose.yml - an app and a database together
services:
  app:
    build: .
    ports:
      - "8080:8080"
    environment:
      DB_HOST: db
    depends_on:
      - db
  db:
    image: postgres:16
    environment:
      POSTGRES_PASSWORD: example
    volumes:
      - db-data:/var/lib/postgresql/data

volumes:
  db-data:

# Start both:  docker compose up -d

Docker or Java First - Decision Sheet

My target role: developer / DevOps / cloud / unsure
Can I write basic programs today?  Y / N
Do I know Linux basics?            Y / N

If "developer" or "unsure" and no coding yet -> Java first
If "DevOps" and basic coding done -> Docker + Linux now
If "DevOps" and no coding -> scripting + language basics first

My decision: _______________

Weekly Plan

Week ___
Main skill: Java / Docker / Linux
Topics: _______________
Practice hours planned: ___   done: ___
Built this week: _______________
One thing I can now explain: _______________

Combined Project Brief

App: Course tracker REST API (Java)
Endpoints: GET /courses, POST /courses
Database: PostgreSQL
Docker:
[ ] Dockerfile for the app
[ ] docker-compose.yml with app + db
[ ] Data kept in a named volume
README:
[ ] How to run with one command
[ ] Diagram of app and database containers