JDK java executable vs JRE executable

Question

I installed the Oracle JDK to /usr/jdk/jdk1.8.0_25 and set that directory to JAVA_HOME. JAVA_HOME/bin contains the java executable and JAVA_HOME/jre/bin contains another java executable. The guide I followed said to add JAVA_HOME/bin and JAVA_HOME/jre/bin to the PATH but which is the correct executable to use and which will be used if I call java from the command line?

Answer 1

Here is a simplified overview of the differences between JDK and JRE

JRE means J ava R untime E nvironment : it contains only binaries for running java program

JDK means J ava D evelopment K it : it contains binaries for running java program + binaries to compile java source code (and produce a java program).

A JDK always contains a JRE inside (under directory <JDK_HOME>/jre )

The major difference between JRE and JDK is the javac program. ( javac means java c ompiler ) (you will also find some other programs under the <JDK_HOME>/bin that aren't present under <JDK_HOME>/jre/bin : all of them may be useful to do java development - but in most case - useless to run a java program.

All programs that are in both locations (ie <JDK_HOME>/bin and <JDK_HOME>/jre/bin ) are the same, so it is not very important to make a distinction.

To answer precisely to your question : the java instance that will run when you execute a command line starting with java is the first instance of java found in your PATH system variable... just like any other program.

Answer 2

Whatever is earlier in the path for java - JAVA_HOME/bin or JAVA_HOME/jre/bin.

If you take a look at the folder structure where jdk / jre is installed you would see that in the jdk/bin folder there are quite a collection of binaries such as java, javac, javap etc. The JRE would include java but not javac, javap etc. I am assuming this is linux and you downloaded the compressed archive and extracted that.

Answer 3

If you are really curious, you can write this to the command line:

where java

This will give the exact location of the executable. On my PC this gives me

C:\ProgramData\Oracle\Java\javapath\java.exe

which is a soft link for the system default runtime java.exe (in my case it is C:\\Program files\\Java\\jre 1.8.0_25\\bin\\java.exe )