Linux which java version change

Switching between Java Versions on Ubuntu linux

If you’re using Ubuntu Linux on your daily basis work, you’ve probably Java installed on your machine. Personally I prefer using Wepupd8 PPA to manage JAVA installation, it makes my life a lot more easier especially for updates. The Wepupd8 team didn’t add any binary for Oracle JAVA installation and they made a script to download the Oracle JAVA from Oracle website and install it straight away. So whenever Oracle will release the update, I can simple upgrade via package manager.

Working with multiple Java versions in your machine is a normal thing, especially if you’re a Java developer, and because I’m a (very) lazy person, I’m always looking for a quicker/easier way to make the switch.

Today, I’ll share with you my tip on this subject. First, let’s run the following command:

$ sudo update-alternatives —config java

Running this command shows a list of installed Java JDKs and JREs allowing one to be selected as the default that is used when java needs to be executed.

But I’m using it just to get the Installation path of each Java version.

Then, for each version I created a script that contain the following lines (in the example below, I’m showing the one for java 8):

Note that I’m using u8.sh to make he switch to Java 8, and u9.sh for Java 9 and so on.
The final step is to add an alias in

/.bashrc file to source our script as follow:

and That’s all. Now for switching between Java versions, I only run u8, u7 or u9 😉

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How to change the default Java version on Ubuntu

If you are a Java developer, it is normal to have multiple Java versions installed on your machine to support different build environments. When a Java program is compiled, the build environment sets the oldest JRE version the program can support. Now, if you run this program on a Linux machine where an unsupported Java version is installed, you will encounter an exception.

For example, if your program is compiled on Java 11, it can’t be run on a machine where Java 8 is installed. But the good thing is you can install multiple Java versions on your machine and quickly change the default JRE version.

In this tutorial, I’ll explain how to change the default Java version on a Linux machine. First of all, run the following command to check the current Java version:

As you can see above, the default Java version is currently set to OpenJDK JRE 1.8. Now, let’s run the following command to see all available Java versions:

Running the above command displays a list of installed Java JDKs and JREs allowing you to select the one as you want to set as default.

When prompted, select the Java version you would like to use. If the list does not include your desired Java version, you can always install it.

Now you can verify the default Java version as fellows:

That’s it. The default Java version is changed to OpenJDK 11.

Bonus: Use Script to Switch Java Version

If you frequently switch between different Java versions, it is a good idea to write a short script to automate the process. Here is the script I used for switching to OpenJDK 8 on my machine.

Similarly, you can create scripts for other Java versions installed on your machine. The next step is to add these scripts as aliases to .bashrc file.

Next, run the following command to load the changes of .bashrc file:

Now if you want to switch to Java 8, just type the following command in your terminal:

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How to change Default Java /JDK Version and ClassPath in Linux using .bash_profile?

Last Updated on October 4th, 2020 by App Shah 2 comments

When you install Java with default apt install command on Ubuntu or CentOS Linux OS then it will install Java under default folder /usr/bin/java .

First thing first. How to install or upgrade JVM in Linux OS?

Please make sure to upgrade to Latest JDK. Today I installed JDK 15. (Oct 2020)

Use below linux command to install latest Java in Ubuntu, CentOS:

# apt install openjdk-9-jre-headless

As you see above, I already have latest JDK 9 installed and then there is no need to download any extra package here. For new re-imaged host it will completely install new Java/JDK binary for you.

After that – just use command which java to find out CLASSPATH variable. In my case it’s /usr/bin/java .

BEFORE:

This is the default Java version available for you to use. With simple command java -version you will see which JDK it referred to.

This is an ideal situation for most of the cases if you are the only one working on project. But it’s not the case for most of the companies out there 🙂

Usually, in production, companies ship Java with their project binary. During runtime they setup CLASSPATH and PATH respectively to use preferred Java version.

Want to change default JVM version in Ubuntu Linux OS? Or CentOS Linux?

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Change Default Java Version on Linux

What is Java?

Java is a general-purpose computer programming language that is concurrent, class-based, object-oriented, and specifically designed to have as few implementation dependencies as possible.

​Article Details

Article is for users which have multiple versions of Java installed in a Linux environment and wish to change the default version from one version of Java to another from a Linux terminal.

Check current version of java being used on system

link currently points to /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.102-4.b14.el7.x86_64/jre/bin/java

Without using grep example

Debian using above command would look like below

java — auto mode
link best version is /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java
link currently points to /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java
link java is /usr/bin/java
slave java.1.gz is /usr/share/man/man1/java.1.gz
/usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java — priority 1081
slave java.1.gz: /usr/lib/jvm/java-8-openjdk-amd64/jre/man/man1/java.1.gz

List Available Java Versions

There are 2 programs which provide ‘java’.

Selection Command
————————————————
1 java-1.7.0-openjdk.x86_64 (/usr/lib/jvm/java-1.7.0-openjdk-1.7.0.111-2.6.7.8.el7.x86_64/jre/bin/java)
*+ 2 java-1.8.0-openjdk.x86_64 (/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.102-4.b14.el7.x86_64/jre/bin/java)

Enter to keep the current selection[+], or type selection number: 2

The left shows *+ meaning it’s the default java version which is 1.8.0. You can change the java version by either typing 1 or 2 at the prompt. Please see above example output.

There is 1 program that provides ‘javac’.

Selection Command
————————————————
*+ 1 java-1.7.0-openjdk.x86_64 (/usr/lib/jvm/java-1.7.0-openjdk-1.7.0.111-2.6.7.8.el7.x86_64/bin/javac)

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

Verify Java Version

openjdk version «1.8.0_102»
OpenJDK Runtime Environment (build 1.8.0_102-b14)
OpenJDK 64-Bit Server VM (build 25.102-b14, mixed mode)

Update Environment

export JAVA_HOME=/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.102-4.b14.el7.x86_64
export PATH=$PATH:$JAVA_HOME/bin

That covers changing the java version of Linux

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Linux which java version change

Java is a programming language originally developed by Sun Microsystems and released in 1995 as a core component of Sun Microsystems’ Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities. Java applications are typically compiled to bytecode that can run on any Java virtual machine (JVM) regardless of computer architecture.

Arch Linux officially supports the open source OpenJDK versions 7, 8, 11 and 16. All these JVM can be installed without conflict and switched between using helper script archlinux-java . Several other Java environments are available in AUR but are not officially supported.

Contents

Installation

Two common packages are respectively pulled as dependency, named java-runtime-common (containing common files for Java Runtime Environments) and java-environment-common (containing common files for Java Development Kits). The provided environment file /etc/profile.d/jre.sh points to a linked location /usr/lib/jvm/default/bin , set by the archlinux-java helper script.

This is used to display and point to a working default Java environment in /usr/lib/jvm/java-$-$ or a Java runtime in /usr/lib/jvm/java-$-$/jre .

Most executables of the Java installation are provided by direct links in /usr/bin , while others are available in $PATH . The script /etc/profile.d/jdk.sh is no longer provided by any package.

OpenJDK

OpenJDK is an open-source implementation of the Java Platform, Standard Edition (Java SE), designated as the official reference implementation. There are several distributors of OpenJDK builds such as AdoptOpenJDK and Amazon Corretto. The Arch Linux OpenJDK packages are built from the upstream OpenJDK source code.

Headless JRE The minimal Java runtime — needed for executing non-GUI Java programs. Full JRE Full Java runtime environment — needed for executing Java GUI programs, depends on headless JRE. JDK Java Development Kit — needed for Java development, depends on full JRE.

Version	Headless JRE	Full JRE	JDK	Documentation	Sources
OpenJDK 16	jre-openjdk-headless	jre-openjdk	jdk-openjdk	openjdk-doc	openjdk-src
OpenJDK 11	jre11-openjdk-headless	jre11-openjdk	jdk11-openjdk	openjdk11-doc	openjdk11-src
OpenJDK 8	jre8-openjdk-headless	jre8-openjdk	jdk8-openjdk	openjdk8-doc	openjdk8-src
OpenJDK 7	jre7-openjdk-headless	jre7-openjdk	jdk7-openjdk	openjdk7-doc	openjdk7-src

OpenJDK GA — Latest OpenJDK General-Availability Release build from Oracle.

OpenJDK EA — Latest OpenJDK Early-Access build for development version from Oracle.

IcedTea-Web — Java Web Start and the deprecated Java browser plugin.

OpenJFX

OpenJFX is the open-source implementation of JavaFX. You do not need to install this package if you are using Oracle JDK. This package only concerns users of the open source implementation of Java (OpenJDK project), and its derivatives.

Version	Runtime and Developement	Documentation	Sources
OpenJFX 16	java-openjfx	java-openjfx-doc	java-openjfx-src
OpenJFX 11	java11-openjfx	java11-openjfx-doc	java11-openjfx-src
OpenJFX 8	java8-openjfx	java8-openjfx-doc	java8-openjfx-src

OpenJFX GA — Latest OpenJFX General-Availability Release build from Gluon.

OpenJFX EA — Latest OpenJFX Early-Access build for development version from Gluon.

Other implementations

Oracle JDK — Oracle’s commercially licensed build of OpenJDK.

OpenJ9 — Eclipse’s implementation of JRE, contributed by IBM.

IBM Certified — IBM Semeru Runtime Certified Edition.

IBM J9 — IBM’s implementation of JRE, using OpenJ9 contributions.

Parrot VM — a VM with experimental support for Java [1] through two different methods: either as a Java VM bytecode translator, or as a Java compiler targeting the Parrot VM.

Development tools

For integrated development environments, see List of applications#Integrated development environments and the Java IDEs subsection specifically.

To discourage reverse engineering an obfuscator like proguard AUR can be used.

Decompilers

• Bytecode Viewer — Java reverse engineering suite, including a decompiler, editor and debugger.

https://bytecodeviewer.com || bytecode-viewerAUR

• CFR — Java decompiler, supporting modern features of Java 9, 10 and beyond.

https://www.benf.org/other/cfr/ || cfrAUR

• Fernflower — Analytical decompiler for Java, developed as part of IntelliJ IDEA.

https://github.com/JetBrains/intellij-community/tree/master/plugins/java-decompiler/engine || fernflower-gitAUR

• JAD — Unmaintained Java decompiler (last release 2006).

https://varaneckas.com/jad || jad

• Java Decompiler (JD-Core, JD-GUI) — Popular Java decompiler providing a GUI and supporting Java 1-10.

https://java-decompiler.github.io/ || jd-guiAUR

• Krakatau — Java decompiler, assembler, and disassembler.

https://github.com/Storyyeller/Krakatau || krakatau-gitAUR

• Procyon decompiler — Experimental Java decompiler, inspired by ILSpy and Mono.Cecil.

https://bitbucket.org/mstrobel/procyon/wiki/Java%20Decompiler || procyon-decompilerAUR , GUI: luytenAUR

Switching between JVM

The helper script archlinux-java provides such functionalities:

List compatible Java environments installed

Note the (default) denoting that java-7-openjdk is currently set as default. Invocation of java and other binaries will rely on this Java install. Also note on the previous output that only the JRE part of OpenJDK 8 is installed here.

Change default Java environment

Note that archlinux-java will not let you set an invalid Java environment. In the previous example, jre8-openjdk is installed but jdk8-openjdk is not so trying to set java-8-openjdk will fail:

Unsetting the default Java environment

There should be no need to unset a Java environment as packages providing them should take care of this. Still should you want to do so, just use command unset :

Fixing the default Java environment

If an invalid Java environment link is set, calling the archlinux-java fix command tries to fix it. Also note that if no default Java environment is set, this will look for valid ones and try to set it for you. Officially supported package «OpenJDK 8» will be considered first in this order, then other installed environments.

Launching an application with the non-default java version

If you want to launch an application with another version of java than the default one (for example if you have both version jre7 and jre8 installed on your system), you can wrap your application in a small bash script to locally change the default PATH of java. For example if the default version is jre7 and you want to use jre8:

Package pre-requisites to support archlinux-java

This section is targeted at packager willing to provide packages in AUR for an alternate JVM and be able to integrate with Arch Linux JVM scheme to use archlinux-java . To do so, packages should:

• Place all files under /usr/lib/jvm/java-$-$
• Ensure all executables for which java-runtime-common and java-environment-common provide links are available in the corresponding package
• Ship links from /usr/bin to executables, only if these links do not already belong to java-runtime-common and java-environment-common
• Suffix man pages with -$$ to prevent conflicts (see jre8-openjdk file list where man pages are suffixed with -openjdk8 )
• Do not declare any conflicts nor replaces with other JDKs, java-runtime , java-runtime-headless nor java-environment
• Use script archlinux-java in install functions to set the Java environment as default if no other valid Java environment is already set (ie: package should not force install as default). See officially supported Java environment package sources for examples

Also please note that:

• Packages that need any Java environment should declare dependency on java-runtime , java-runtime-headless or java-environment as usual
• Packages that need a specific Java vendor should declare dependency on the corresponding package
• OpenJDK packages now declare provides=»java-runtime-openjdk=$» etc. This enables a third-party package to declare dependency on an OpenJDK without specifying a version

Troubleshooting

MySQL

Due to the fact that the JDBC-drivers often use the port in the URL to establish a connection to the database, it is considered «remote» (i.e., MySQL does not listen to the port as per its default settings) despite the fact that they are possibly running on the same host, Thus, to use JDBC and MySQL you should enable remote access to MySQL, following the instructions in MariaDB#Grant remote access.

IntelliJ IDEA

If IntelliJ IDEA outputs The selected directory is not a valid home for JDK with the system Java SDK path, you may have to install a different JDK package and select it as IDEA’s JDK.

Impersonate another window manager

You may use the wmname from suckless.org to make the JVM believe you are running a different window manager. This may solve a rendering issue of Java GUIs occurring in window managers like Awesome or Dwm or Ratpoison. Try set «compiz» or «LG3D»

You must restart the application in question after issuing the wmname command.

This works because the JVM contains a hard-coded list of known, non-re-parenting window managers. For maximum irony, some users prefer to impersonate LG3D , the non-re-parenting window manager written by Sun, in Java.

Illegible fonts

In addition to the suggestions mentioned below in #Better font rendering, some fonts may still not be legible afterwards. If this is the case, there is a good chance Microsoft fonts are being used. Install ttf-ms-fonts AUR .

Missing text in some applications

If some applications are completely missing texts it may help to use the options under #Tips and tricks as suggested in FS#40871.

Gray window, applications not resizing with WM, menus immediately closing

The standard Java GUI toolkit has a hard-coded list of «non-reparenting» window managers. If using one that is not on that list, there can be some problems with running some Java applications. One of the most common problems is «gray blobs», when the Java application renders as a plain gray box instead of rendering the GUI. Another one might be menus responding to your click, but closing immediately.

There are several things that may help:

• For jre7-openjdk or jre8-openjdk , append the line export _JAVA_AWT_WM_NONREPARENTING=1 in /etc/profile.d/jre.sh . Then, source the file /etc/profile.d/jre.sh or log out and log back in.
• For last version of JDK append line export AWT_TOOLKIT=MToolkit in

/.xinitrc before exec window manager.
Also, we can try to use wmname with line wmname compiz in your

/.xinitrc .

For Oracle’s JRE/JDK, use SetWMName. However, its effect may be canceled when also using XMonad.Hooks.EwmhDesktops . In this case, appending >> setWMName «LG3D» to the LogHook may help.

For sway, export _JAVA_AWT_WM_NONREPARENTING=1 may solve the problem.

See [2] for more information.

System freezes when debugging JavaFX Applications

If your system freezes while debugging a JavaFX Application, you can try to supply the JVM option -Dsun.awt.disablegrab=true .

JavaFX’s MediaPlayer constructor throws an exception

Creating instance of MediaPlayer class from JavaFX’s sound modules might throw following exception (both Oracle JDK and OpenJDK)

which is a result of some incompatibilities of JavaFX with modern ffmpeg build delivered within Arch Linux repository.

Working solution is to install ffmpeg-compat-55 AUR .

Java applications cannot open external links

If a Java application is not able to open a link to, for example, your web browser, install gvfs . This is required by the Desktop.Action.BROWSE method. See [3]

Error initializing QuantumRenderer: no suitable pipeline found

Possible issues / solutions:

• GTK2 is missing. Install gtk2
• OpenJFX is missing. Install java-openjfx

Tips and tricks

Behavior of most Java applications can be controlled by supplying predefined variables to Java runtime. From this forum post, a way to do it consists of adding the following line in your

/.bash_profile (or /etc/profile.d/jre.sh to affect programs that are not run by sourcing

For example, to use system anti-aliased fonts and make swing use the GTK look and feel:

Three such variables exist, the options which are explained later in the table below take priority.

JAVA_TOOL_OPTIONS	Affects applications as well as tools like javac or the jshell.
JDK_JAVA_OPTIONS	Affects applications (everything started via the java command). Requires Java 9.
(command line options)	Arguments specified before the «class name» argument are Java options.
_JAVA_OPTIONS	The old way, affects applications and tools.

Better font rendering

Both closed source and open source implementations of Java are known to have improperly implemented anti-aliasing of fonts. This can be fixed with the following options: -Dawt.useSystemAAFontSettings=on , -Dswing.aatext=true

See Java Runtime Environment fonts for more detailed information.

Silence ‘Picked up JDK_JAVA_OPTIONS’ message on command line

Setting the JDK_JAVA_OPTIONS environment variables makes java (openjdk) write to stderr messages of the form: ‘Picked up JDK_JAVA_OPTIONS=. ‘. To suppress those messages in your terminal you can unset the environment variable in your

/.bashrc and alias java to pass those same options as command line arguments:

Non interactive shells, like the launcher scripts for Java programs, (usually) do not read the

/.bashrc , but still inherited exported variables from their parent process (which in turn inherited it at some point from the login shell which read the

/.bash_profile ). As for the cases when they do, one put’s generally a statement at the op of the

/.bashrc to avoid the file being read. That way, the variables are passed to programs launched via the desktop menu and in the case of an interactive shell where the message would disturb aliases are used instead (which in turn cannot be used in scripts).

GTK LookAndFeel

If your Java programs look ugly, you may want to set up the default look and feel for the swing components:

Some Java programs insist on using the cross platform Metal look and feel. In some of these cases you can force these apps to use the GTK look and feel by setting the following property:

GTK3 Support

In Java releases prior to version 9, the GTK LookAndFeel is linked against GTK2, whilst many newer desktop applications use GTK3. This incompatibility between GTK versions may break applications utilizing Java plugins with GUI, as the mixing of GTK2 and GTK3 in the same process is not supported (for example, LibreOffice 5.0).

The GTK LookAndFeel can be run against GTK versions 2 , 2.2 and 3 , defaulting to GTK3. This can be overridden by setting the following property:

Better 2D performance

Switching to OpenGL-based hardware acceleration pipeline will improve 2D performance

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