MATLAB

find where JAVA_HOME is set

grep JAVA_HOME /etc/environment /etc/bash.bashrc /etc/profile.d/* /etc/profile

java home

chmod 755 gradlew
echo $JAVA_HOME

what is java_home

JAVA_HOME is an operating system (OS) environment variable which can optionally be set after either the Java Development Kit (JDK) or the Java Runtime Environment (JRE) is installed. The JAVA_HOME environment variable points to the file system location where the JDK or JRE was installed.

java_home what is

Optional.

The JAVA_HOME environment variable points to the file system location where 
the JDK (Usually only JDK not JRE) installed.

Avoid using it. Prefer to have your java in PATH or managed by something like JVMS