The preferred way to install and manage Java JDKs on Linux

I'm on Fedora Workstation 40, but similar steps would work on most major Linux distros like Ubuntu/Mint etc

Check existing Java installation

On some Linux distros, Java comes installed by default; however it is just the JRE and not the JDK. You can verify this as java command is found but the javac command is NOT found.

java  # would show manual of arguments
javac # would give not found error if JDK not installed

java --version  # OR "java -version" for older java
javac --version

Refer these articles to know the differences between JDK, JRE and JVM:

• Java Programming Environment and the Java Runtime Environment (JRE)
• What are JDK, JRE, JVM and JIT in Java?

In Fedora, the JREs/JDKs are stored within /usr/lib/jvm. So you can look into it's contents or query them as:

find /usr/lib/jvm -name java
find /usr/lib/jvm -name javac

Installing an OpenJDK

I'm on Fedora 40 where the package manager is dnf. You would be installing your desired OpenJDK via your respective Linux distro's package manager (like apt for Ubuntu/Debian):

• Search available JDKs to install:

  dnf search jdk

You would get a list of packages available to install having various Java versions as well as the variant suffix in the package. The headless variants usually just include the JRE. To install the full JDK with all the necessary tools for Java development, we need the development variant of the package, usually containing the -devel term suffix in the name for dnf. Here's a list of few package variant names for Java 17 OpenJDK from the dnf output:

  java-17-openjdk.x86_64 : OpenJDK 17 Runtime Environment
  java-17-openjdk-devel.x86_64 : OpenJDK 17 Development Environment
  java-17-openjdk-devel-fastdebug.x86_64 : OpenJDK 17 Development Environment optimised with full debugging on
  java-17-openjdk-devel-slowdebug.x86_64 : OpenJDK 17 Development Environment unoptimised with full debugging on
  java-17-openjdk-fastdebug.x86_64 : OpenJDK 17 Runtime Environment optimised with full debugging on
  java-17-openjdk-headless.x86_64 : OpenJDK 17 Headless Runtime Environment
  java-17-openjdk-headless-fastdebug.x86_64 : OpenJDK 17 Runtime Environment optimised with full debugging on
  java-17-openjdk-headless-slowdebug.x86_64 : OpenJDK 17 Runtime Environment unoptimised with full debugging on
  java-17-openjdk-javadoc.x86_64 : OpenJDK 17 API documentation
  java-17-openjdk-portable.x86_64 : OpenJDK 17 Runtime Environment portable edition
  java-17-openjdk-portable-devel.x86_64 : OpenJDK 17 Development Environment portable edition
  java-17-openjdk-portable-sources.x86_64 : OpenJDK 17 full patched sources of portable JDK
  java-17-openjdk-slowdebug.x86_64 : OpenJDK 17 Runtime Environment unoptimised with full debugging on
  java-17-openjdk-src.x86_64 : OpenJDK 17 Source Bundle
  java-17-openjdk-src-fastdebug.x86_64 : OpenJDK 17 Source Bundle for packages with debugging on and optimisation
  java-17-openjdk-src-slowdebug.x86_64 : OpenJDK 17 Source Bundle for packages with debugging on and no optimisation

On Ubuntu,, there are lesser packages and the one you want to install is typically named like openjdk-17-jdk for the whole JDK toolset

• Install your desired OpenJDK package from that list

  # Installing the latest OpenJDK with optimized debugging
  sudo dnf install java-latest-openjdk-devel-fastdebug

  # Installing a specific version like OpenJDK 17
  sudo dnf install java-17-openjdk-devel

• Verify installation by checking java and javac commands are found

Installing an Oracle JDK

• Visit the Official Oracle SE Downloads Page. Locate your required Java version's downloads section

• Download the appropriate package for your platform. For RedHat based Linux distros like Fedora, download the .rpm package (and .deb for Ubuntu/Debian). Before downloading, you'll have to sign-in to Oracle and agree to the terms

• Double click on the downloaded file (like jdk-11.0.24_linux-x64_bin.rpm) and select Install. It will install and configure the Oracle JDK.

• Now that OracleJDK is installed, verify the java and javac commands being detected

Installing JDKs via IntelliJ

You can also install JDKs from within IntelliJ itself:

• Click on the Gear icon ⚙️ and then go into Project Structure. Select SDKs, click + plus icon. Then select the JDK you wish to be downloaded and installed
• The JDK is installed in the ~/.jdks folder, for example: ~/.jdks/openjdk-20.0.2/

IntelliJ auto-detects your available JDK locations on your system. You can also add your existing JDK folder locations like /usr/lib/jvm/jdk-11-oracle-x64 under configured JDKs in Project Structure

Working with multiple Java installations

The update-alternatives command in Linux (also called just alternatives in Fedora) creates, removes, maintains and displays information about the symbolic links comprising the alternatives system.

It is possible for several programs fulfilling the same or similar functions to be installed on a single system at the same time. A generic name in the filesystem is shared by all files providing interchangeable functionality. The alternatives system helps determine which actual file is referenced by this generic name.

Useful references:

• update-alternatives - Linux manpage
• Introduction to the alternatives command in Linux - RedHat

When you install OpenJDK via your package manager or Oracle-JDK from the downloaded file, the alternatives should automatically get updated during that process

View available options for a command

update-alternatives --display java

The output would look like:

java - status is manual.
 link currently points to /usr/lib/jvm/java-21-openjdk-21.0.4.0.7-2.fc40.x86_64/bin/java
/usr/lib/jvm/java-21-openjdk-21.0.4.0.7-2.fc40.x86_64/bin/java - family java-21-openjdk.x86_64 priority 21000407
 ... follower links ...
/usr/lib/jvm/jdk-11.0.24-oracle-x64/bin/java - priority 184745984
 ... follower links ...
/usr/lib/jvm/java-22-openjdk-22.0.2.0.9-1.rolling.fc40.x86_64-fastdebug/bin/java - family java-latest-openjdk.x86_64 priority 1
 ... follower links ...
Current `best' version is /usr/lib/jvm/jdk-11.0.24-oracle-x64/bin/java.

Similarly, see alternative options list for javac

Adding an alternatives entry for a command

If any alternative for your commands is NOT registered in the list, you can manually add them as:

sudo update-alternatives --install <link> <name> <path> <priority>

For example, I downloaded the JetBrains Runtime (JCEF) JDK from within IntelliJ, which was downloaded at ~/.jdks/jbrsdk_jcef-17.0.12/ folder; but it was not showing up in the alternatives list. So, I'll add the alternatives entry for java and javac as:

sudo update-alternatives --install /usr/bin/java java ~/.jdks/jbrsdk_jcef-17.0.12/bin/java 138
sudo update-alternatives --install /usr/bin/javac javac ~/.jdks/jbrsdk_jcef-17.0.12/bin/javac 138

Similarly, add alternatives for more commands like jar, javadoc etc. as required

You can also add follower links as:

--install link name path priority [--follower link name path]... [--initscript service] [--family name]

Switching between available alternatives of a command

Pick between Java installations present

sudo update-alternatives --config java

The output would look like below. Note that * denotes best available version and + denotes your current selection:

There are 4 programs which provide 'java'.

  Selection    Command
-----------------------------------------------
 + 1           java-latest-openjdk.x86_64 (/usr/lib/jvm/java-23-openjdk-23.0.0.0.37-1.rolling.fc40.x86_64-fastdebug/bin/java)
*  2           /usr/lib/jvm/jdk-11.0.24-oracle-x64/bin/java
   3           java-21-openjdk.x86_64 (/usr/lib/jvm/java-21-openjdk-21.0.5.0.11-1.fc40.x86_64/bin/java)
   4           /home/kumar/.jdks/jbrsdk_jcef-17.0.12/bin/java

Enter to keep the current selection[+], or type selection number:

Similarly, choose among the alternative options for javac

When you uninstall/remove your JDK packages, remember to delete the respective alternatives entries too

Removing an alternatives entry

For example, to remove the JCEF JDK's java command alternative entry:

sudo update-alternatives --remove java ~/.jdks/jbrsdk_jcef-17.0.12/bin/java

Add Java to PATH

This should not be necessary if you are following the update-alternatives method to manage between Java installations and all entries are complete

However, to manually set the configuration in your shell profile, you can do as below:

• Set Environment Variables in your Shell config file (i.e. ~/.zshrc, ~/.bashrc etc.)

  # Set "JAVA_HOME" environment variable to the jdk folder path
  export JAVA_HOME=/usr/lib/jvm/jdk-11-oracle-x64
  # Add the binaries within JAVA_HOME like 'java', 'javac' to PATH
  export PATH=$PATH:$JAVA_HOME/bin

• Restart SHELL:

  exec $(which $SHELL)

• Now, java should be detected successfully

  [kumar@lenovo-s340 ~]$ java --version
  java 11.0.22 2024-01-16 LTS
  Java(TM) SE Runtime Environment 18.9 (build 11.0.22+9-LTS-219)
  Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.22+9-LTS-219, mixed mode)
  [kumar@lenovo-s340 ~]$ javac --version
  javac 11.0.22