How to downgrade Java from 9 to 8 on a MACOS. Eclipse is not running with Java 9

How to downgrade Java from 9 to 8 on a macOS Sierra 10.12.6(16G29) . I tried removing the Java plugin and installed Java 8, however the Java and javac version shows 9 in terminal, but In system preferences it is 8.

You don't need to down grade. You can run more than one version of Java on MacOS. You can set the version of your terminal with this command in MacOS.

# List Java versions installed
/usr/libexec/java_home -V

# Java 11
export JAVA_HOME=$(/usr/libexec/java_home -v 11)

# Java 1.8
export JAVA_HOME=$(/usr/libexec/java_home -v 1.8)

# Java 1.7
export JAVA_HOME=$(/usr/libexec/java_home -v 1.7)

# Java 1.6
export JAVA_HOME=$(/usr/libexec/java_home -v 1.6)

You can set the default value in the .bashrc, .profile, or .zprofile

This is how I did it. You don't need to delete Java 9 or newer version.

Step 1: Install Java 8

You can download Java 8 from here: http://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html

Step 2: After installation of Java 8. Confirm installation of all versions.Type the following command in your terminal.

/usr/libexec/java_home -V

Step 3: Edit .bash_profile

sudo nano ~/.bash_profile

Step 4: Add 1.8 as default. (Add below line to bash_profile file).

export JAVA_HOME=$(/usr/libexec/java_home -v 1.8)

Now Press CTRL+X to exit the bash. Press 'Y' to save changes.

Step 5: Reload bash_profile

source ~/.bash_profile

Step 6: Confirm current version of Java

java -version

If you have multiple Java versions installed on your Mac, here's a quick way to switch the default version using Terminal. In this example, I am going to switch Java 10 to Java 8.

$ java -version
java version "10.0.1" 2018-04-17
Java(TM) SE Runtime Environment 18.3 (build 10.0.1+10)
Java HotSpot(TM) 64-Bit Server VM 18.3 (build 10.0.1+10, mixed mode)

$ /usr/libexec/java_home -V
Matching Java Virtual Machines (2):
    10.0.1, x86_64:	"Java SE 10.0.1"	/Library/Java/JavaVirtualMachines/jdk-10.0.1.jdk/Contents/Home
    1.8.0_171, x86_64:	"Java SE 8"	/Library/Java/JavaVirtualMachines/jdk1.8.0_171.jdk/Contents/Home

/Library/Java/JavaVirtualMachines/jdk-10.0.1.jdk/Contents/Home

Then, in your .bash_profile add the following.

# Java 8
export JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk1.8.0_171.jdk/Contents/Home

Now if you try java -version again, you should see the version you want.

$ java -version
java version "1.8.0_171"
Java(TM) SE Runtime Environment (build 1.8.0_171-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.171-b11, mixed mode)

As it allows to install more than one version of java, I had install many 3 versions unknowingly but it was point to latest version "11.0.2"

I could able to solve this issue with below steps to move to "1.8"

$java -version

openjdk version "11.0.2" 2019-01-15 OpenJDK Runtime Environment 18.9 (build 11.0.2+9) OpenJDK 64-Bit Server VM 18.9 (build 11.0.2+9, mixed mode)

cd /Library/Java/JavaVirtualMachines
ls

jdk1.8.0_201.jdk jdk1.8.0_202.jdk openjdk-11.0.2.jdk

sudo rm -rf openjdk-11.0.2.jdk
sudo rm -rf jdk1.8.0_201.jdk
ls

jdk1.8.0_202.jdk

java -version

java version "1.8.0_202-ea" Java(TM) SE Runtime Environment (build 1.8.0_202-ea-b03) Java HotSpot(TM) 64-Bit Server VM (build 25.202-b03, mixed mode)

Old question but just had that problem /dumb jira having problems with java 10/ and didn't find a simple answer here so just gonna leave it:

$ /usr/libexec/java_home -V shows the versions installed and their locations so you can simply remove /Library/Java/JavaVirtualMachines/<the_version_you_want_to_remove>. Voila

The simplest solution might be to install Java 8 in parallel to Java 9 (if not still still existant) and specify the JVM to be used explicitly in eclipse.ini. You can find a description of this setting including a description how to find eclipse.ini on a Mac at Eclipsepedia

As mentioned in the offical Oracle Documentation there are two relevant paths you need to delete in case you wan't to remove a Java installation.

Path 1 is the JRE - installation path: /Library/Internet Plug-Ins/
Path 2 is the JDK - installation path: /Library/Java/JavaVirtualMachines

JRE Steps:
Change directory via Terminal to the Path 1.

cd /Library/Internet Plug-Ins/

Remove JavaAppletPlugin.plugin

sudo rm -rf JavaAppletPlugin.plugin

JDK Steps:
Do the Steps under JRE Steps
Change directory via Terminal to the Path 2.

/Library/Java/JavaVirtualMachines

Take a look at all installations at this folder

ls

Remove any installations in this folder.

sudo rm -rf /Library/Java/JavaVirtualMachines/jdk-(...).jdk

After uninstalling you are ready to go for a fresh installation. Just download you're version of choice and install it.

# List Java versions installed
/usr/libexec/java_home -V

# Java 11
export JAVA_HOME=$(/usr/libexec/java_home -v 11)

# Java 1.8
export JAVA_HOME=$(/usr/libexec/java_home -v 1.8)

# Java 1.7
export JAVA_HOME=$(/usr/libexec/java_home -v 1.7)

# Java 1.6
export JAVA_HOME=$(/usr/libexec/java_home -v 1.6)

You can remove "JavaAppletPlugin.plugin" found in Spotlight or Finder, then re-install downloaded Java 8.

This will simply solve your problem.