java-tutorial

1) Getting Started

Goal

• Install a JDK
• Compile and run a Java program
• Understand what javac and java do

Install the JDK (recommended: Java 17 or 21)

• Install a JDK from a reputable provider (e.g., Adoptium Temurin).
• Verify installation:

PowerShell:

java -version
javac -version

If those commands are not found, your PATH is not set.

Your first program

Create a file named Hello.java:

public class Hello {
    public static void main(String[] args) {
        System.out.println("Hello, Java!");
    }
}

Compile:

javac Hello.java

Run:

java Hello

What just happened?

• javac compiles .java source code into .class bytecode.
• java runs bytecode on the JVM (Java Virtual Machine).

Exercises

1. Change the message and re-run.
2. Print two lines.
3. Print your name using args:
   • Run java Hello Alice and print Alice.

Common mistakes

• File name and public class name must match (Hello.java and public class Hello).
• Don’t run java Hello.java (that’s not how the classic compile/run flow works).

Table of contents

1. Getting Started: Install, run, and your first program
2. Java Basics: types, variables, operators, formatting
3. Control Flow: if/switch/loops
4. Methods: parameters, return values, overloading
5. OOP: classes, objects, encapsulation
6. Inheritance & Polymorphism (and when not to use them)
7. Interfaces, abstract classes, and design basics
8. Exceptions and error handling
9. Strings, files, and I/O basics
10. Collections: List/Set/Map and Big-O intuition
11. Generics (the useful parts)
12. Lambdas & Streams
13. Dates and time (java.time)
14. Testing with JUnit 5 (basics)
15. Concurrency: threads, executors, futures
16. JVM basics: memory, GC, performance habits
17. Build tools: Maven essentials (recommended)
18. Next steps: projects to build