Install the JDK & Set Up

Before you can write Java, you need a JDK (Java Development Kit) on your computer. In this lesson you will install Java 25 LTS, make sure your terminal can find it, try out Java's interactive shell, and choose an editor.

The whole process takes about ten minutes. Most problems beginners face later ("javac is not recognized", "wrong version") come from a messy setup, so it is worth doing carefully once.

Choose a JDK build

Java's source code lives in the open-source OpenJDK project. Several companies build installers from that same code. They behave the same way for learning, so pick one and move on.

Always choose version 25 (the current LTS) and the JDK, not a JRE.

Install on Windows

The simplest way is the official MSI installer from adoptium.net. Choose Windows, x64 (or aarch64 for ARM laptops), JDK, version 25, and download the .msi file. While installing:

• Keep Add to PATH switched on (it is on by default).
• Switch on Set JAVA\_HOME variable. It is off by default, and build tools such as Maven look for it.

If you prefer the command line, Windows 10 and 11 include the winget package manager. Open PowerShell and run:

winget install EclipseAdoptium.Temurin.25.JDK

Close and reopen your terminal after installing, so it picks up the new PATH.

Install on macOS and Linux

On macOS you can use the .pkg installer from adoptium.net, or Homebrew:

brew install --cask temurin@25

On Ubuntu 26.04 LTS, Java 25 is the default JDK, so either command below works. On other distributions, use your package manager or the packages listed on adoptium.net.

sudo apt update
sudo apt install openjdk-25-jdk

Check your installation

Open a new terminal and ask both the runtime and the compiler for their versions:

java -version
javac -version

You should see a version starting with 25. The exact update number and date change every three months, so yours may differ. In October 2026 the Temurin output looks like this:

openjdk version "25.0.5" 2026-10-20 LTS
OpenJDK Runtime Environment Temurin-25.0.5+8 (build 25.0.5+8-LTS)
OpenJDK 64-Bit Server VM Temurin-25.0.5+8 (build 25.0.5+8-LTS, mixed mode, sharing)
javac 25.0.5

If javac prints "not recognized" or "command not found", the JDK's bin folder is not on your PATH. If java -version shows an old version such as 1.8.0, an older Java is earlier on your PATH.

JAVA_HOME and PATH explained

Two environment variables matter:

• PATH is the list of folders your terminal searches when you type a command. The JDK's bin folder (which holds java.exe and javac.exe) must be in it.
• JAVA\_HOME points to the JDK folder itself (the parent of bin). Maven, Gradle and many IDEs read it to find Java.

On Windows, this PowerShell snippet shows both and lists every java.exe the system can find. The first one listed is the one that runs.

$env:JAVA_HOME
where.exe java

On a laptop that once had Oracle Java 8, the output might look like this:

C:\Program Files\Eclipse Adoptium\jdk-25.0.5.8-hotspot\
C:\Program Files\Common Files\Oracle\Java\javapath\java.exe
C:\Program Files\Eclipse Adoptium\jdk-25.0.5.8-hotspot\bin\java.exe

Here the old Oracle javapath folder comes first, so typing java runs Java 8. Fix it by uninstalling the old Java from Settings > Apps, or by moving the JDK 25 bin entry above it in System Properties > Environment Variables > Path. Then open a new terminal and check again.

Try Java instantly with JShell

The JDK includes JShell, an interactive shell (a REPL: read, evaluate, print, loop). You type a line of Java and see the result at once, without writing a class or compiling. It is perfect for testing small ideas. Start it by typing jshell, and leave with /exit.

jshell> 7 * 24
$1 ==> 168

jshell> String city = "Kochi"
city ==> "Kochi"

jshell> city.length()
$3 ==> 5

jshell> city.toUpperCase()
$4 ==> "KOCHI"

JShell stores each result in a variable such as $1, so you can reuse it. You will use JShell throughout this course to check small facts quickly.

Choose an editor

You can write Java in any text editor, but a Java-aware editor underlines mistakes as you type, completes method names and runs programs with one click.

• IntelliJ IDEA from JetBrains: the most popular Java IDE, with a free edition that covers this whole course.
• VS Code with Microsoft's Extension Pack for Java: lighter, good if you already use VS Code.
• Eclipse IDE: free and open source, still common in colleges and companies.

For the first few lessons, use the terminal and a plain editor. Typing javac and java yourself teaches you what an IDE does behind the scenes.

Common mistakes

• Not reopening the terminal. A terminal keeps the PATH it had when it opened. After installing, always open a new one.
• Two Java versions fighting. Use where.exe java (Windows) or which -a java (Linux, macOS) to see every copy and which one wins.
• JAVA\_HOME pointing at bin. It must point to the JDK folder, such as C:\Program Files\Eclipse Adoptium\jdk-25.0.5.8-hotspot, not to its bin subfolder.
• Installing a JRE by mistake. If java -version works but javac does not exist, you installed a runtime only. Install the JDK.

Key points

• Install a JDK for Java 25 LTS; Eclipse Temurin, Oracle, Amazon and Microsoft builds all come from OpenJDK.
• On Windows use the MSI (switch on "Set JAVA\_HOME variable") or winget install EclipseAdoptium.Temurin.25.JDK.
• Check with java -version and javac -version; both should start with 25.
• PATH must contain the JDK's bin folder; JAVA\_HOME must point to the JDK folder.
• JShell lets you run single lines of Java instantly.

jshell> 7 * 24 * 60
$1 ==> 10080

jshell> String city = "Pune"
city ==> "Pune"

jshell> city.toUpperCase()
$3 ==> "PUNE"