How to tell if JRE or JDK is installed

I have one computer that I intentionally installed JDK on. I have another computer with JRE, for, among other things, testing. However, when I got a java application working on this computer, and then tried it on another, it complained that JDK was required. How can I check if JDK was somehow installed on my system? Note: the computer in question is a Mac.

Solution 1:

You can open up terminal and simply type

java -version // this will check your jre version
javac -version // this will check your java compiler version if you installed 

this should show you the version of java installed on the system (assuming that you have set the path of the java in system environment).

And if you haven't, add it via

export JAVA_HOME=/path/to/java/jdk1.x

and if you unsure if you have java at all on your system just use find in terminal

i.e. find / -name "java"

Solution 2:

Normally a jdk installation has javac in the environment path variables ... so if you check for javac in the path, that's pretty much a good indicator that you have a jdk installed.

Solution 3:

@maciej-cygan described the process well, however in order to find your java path:

$ which java

it gives you the path of java binary file which is a linked file in /usr/bin directory. next:

$ cd /usr/bin/ && ls -la | grep java

find the pointed location which is something as follows (for me):

then cd to the pointed directory to find the real home directory for Java. next:

$ ls -la | grep java

which is as follows in this case:

so as it's obvious in the screenshot, my Java home directory is /usr/lib/jvm/java-11-openjdk-amd64. So accordingly I need to add JAVA_HOME to my bash profile (.bashrc, .bash_profile, etc. depending on your OS) like below:

JAVA_HOME="/usr/lib/jvm/java-11-openjdk-amd64"

Here you go!