Installing Java and your first program

Kabir's first “Hello”

What does “setting up Java” mean?

Words you'll meet in this lesson

Setup checklist

Ways to write and run Java

Choose your editor

Four ways to run your program

Install, check, write, compile, run

1. Install the JDK

   Download Eclipse Temurin 21 (LTS) for your operating system from adoptium.net and run the installer. On Windows, tick the options “Set JAVA_HOME variable” and “Add to PATH” if the installer offers them.

   The installer copies the JDK folder (bin, lib, conf…) to a location like C:\Program Files\Eclipse Adoptium\jdk-21… on Windows or /Library/Java/JavaVirtualMachines/ on macOS.

2. Set JAVA_HOME and PATH (if not done)

   Windows: search “Environment Variables” → New system variable JAVA_HOME = the JDK folder → edit Path → add %JAVA_HOME%\bin and move it to the top. macOS/Linux: add these lines to ~/.zshrc or ~/.bashrc:

   export JAVA_HOME=$(/usr/libexec/java_home -v 21)   # macOS
   export PATH="$JAVA_HOME/bin:$PATH"

   PATH is searched from first folder to last. Putting the JDK's bin first makes sure your terminal uses this JDK even if an older Java exists elsewhere.

3. Open a NEW terminal and check

   java -version
   javac -version

   Terminals read environment variables only when they start, so an old window won't see your changes. Both commands should show the same version.

4. Write your first program

   Make a folder such as C:\java-practice, open it in your editor, and create Hello.java:

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

   Namaste, MyPhatshala!
   The editor saves plain text. Use “Save as” and check the name really is Hello.java, not Hello.java.txt (Windows can hide extensions).

5. Compile and run

   cd C:\java-practice
   javac Hello.java
   java Hello

   Namaste, MyPhatshala!
   cd moves into your folder, because javac and java look for files in the current folder. javac writes Hello.class; java Hello asks the JVM to load the class named Hello and run its main.

From installer to first output: both views

Six moments in Kabir's setup. Left: his screen. Right: what the operating system and Java are doing.

How developers set up Java at work

At home you install one JDK. At work, setups are a little more organised. Here's what you'll meet in your first job.

Watch it with an example: two commands in the terminal

Riya's folder and terminal, side by side. See which file each command needs and what it creates.

Examples are simplified. Every company has its own setup guide; read it on your first day.

Your first real programs

Here's a slightly bigger first program with notes. The live editor uses the class name Main, so the challenges do too.

public class Hello {
    public static void main(String[] args) {
        System.out.println("Namaste, MyPhatshala!");
        System.out.println("Arguments received: " + args.length);
        System.out.println("Java\tis\tfun");
    }
}

• public class HelloThe class name. Save the file as Hello.java, with a capital H.
• String[] argsHolds any words typed after the class name. java Hello Riya Kharghar would make args.length 2.
• args.lengthHow many arguments arrived. With plain java Hello it's 0.
• "Java\tis\tfun"\t is an escape sequence for a tab. Others: \n new line, \" a double quote, \\ a backslash.

What the JVM does with your first program

Step through Hello.java. Watch where args comes from and how each line reaches the console.

Worked examples: real problems, solved and traced in memory

Your first programs mostly print. These three show the printing tools you'll use for years: println vs print, escape sequences like \t and \n, and the args array that receives command-line input.

PNR 4521789630, train 12123 Deccan Queen, coach C2 seat 34

==== E-TICKET ====
PNR:	4521789630
Train:	12123 "Deccan Queen"
Coach:	C2
Seat:	34
==================

Pen × 3 Rs 30, Notebook × 2 Rs 90

Pen x3 Rs 30
Notebook x2 Rs 90
Total Rs 120

run as: java Main (no extra words)

Arguments received: 0
Is args null? false
Try: java Main Asha 3

Check yourself

Quick revision

Interview and viva questions

Practice problems

Practise printing exactly what you want: lines, tabs, quotes and numbers. Every output is fixed. The last three are business tasks.

(none)

Hello
Namaste
Vanakkam

public class Main {
    public static void main(String[] args) {
        System.out.println("Hello\nNamaste\nVanakkam");
    }
}

(none)

She said "Java is easy".

public class Main {
    public static void main(String[] args) {
        System.out.println("She said \"Java is easy\".");
    }
}

(none)

1 2 3

public class Main {
    public static void main(String[] args) {
        System.out.print("1 ");
        System.out.print("2 ");
        System.out.print("3");
        System.out.println();
    }
}

Tea 15, Coffee 25

Item	Price
Tea	15
Coffee	25

public class Main {
    public static void main(String[] args) {
        System.out.println("Item\tPrice");
        System.out.println("Tea\t15");
        System.out.println("Coffee\t25");
    }
}

(none)

C:\Java\bin

public class Main {
    public static void main(String[] args) {
        System.out.println("C:\\Java\\bin");
    }
}

(none)

========================
  Sharma General Store
========================

public class Main {
    public static void main(String[] args) {
        System.out.println("========================");
        System.out.println("  Sharma General Store");
        System.out.println("========================");
    }
}

450

Total: Rs 450

public class Main {
    public static void main(String[] args) {
        int total = 450;
        System.out.print("Total: Rs ");
        System.out.println(total);
    }
}

run with no arguments

Got 0 of 2 arguments
Missing: 2

public class Main {
    public static void main(String[] args) {
        System.out.println("Got " + args.length + " of 2 arguments");
        System.out.println("Missing: " + (2 - args.length));
    }
}

Real-world scenario questions (asked in company interviews)

Setup problems are some of the first things you'll solve in a new job. Decide your answer first, then open the model answer.