Install JDK 21

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Goal

Install the Java Development Kit version 21. After this page you will have a working java and javac on your PATH.

Prerequisites

• None. This is the first page of the Beginner tier.

What the JDK is

The JDK (Java Development Kit) is two things in one: the JVM (Java Virtual Machine — the runtime that executes Java programs) and the compiler (javac, which turns .java source files into .class bytecode).

We pin to JDK 21 because it is the current long-term support release. Spring Boot 3.4 supports it cleanly. Older JDKs still work but the language features in this tier (records, var) need at least 17.

There are several distributions of the JDK. They are all the same Java — different packagers. Pick one:

• Temurin from Eclipse Adoptium — the default for most developers.
• Microsoft Build of OpenJDK — if you live in the Microsoft ecosystem.
• Amazon Corretto — if you deploy on AWS.

For everything else about distributions, see the Adoptium FAQ.

Install

On macOS with Homebrew:

brew install --cask temurin@21

On Ubuntu / Debian:

sudo apt update
sudo apt install -y temurin-21-jdk

If apt does not know about temurin-21-jdk, follow the Adoptium apt instructions to add their repo first.

On Windows, download the MSI installer from adoptium.net and run it.

Verify

java -version

Expected output (vendor string may differ):

openjdk version "21.0.5" 2024-10-15 LTS
OpenJDK Runtime Environment Temurin-21.0.5+11 (build 21.0.5+11-LTS)
OpenJDK 64-Bit Server VM Temurin-21.0.5+11 (build 21.0.5+11-LTS, mixed mode, sharing)

The first line must say 21. If it says 17, 11, or 1.8, an older JDK is shadowing 21 on your PATH — fix that before moving on.

javac -version

javac 21.0.5

Next → Install Maven