How do I set the default Java installation/runtime (Windows)?

This is a bit of a pain on Windows. Here's what I do.

Install latest Sun JDK, e.g. 6u11, in path like c:\install\jdk\sun\6u11, then let the installer install public JRE in the default place (c:\program files\blah). This will setup your default JRE for the majority of things.

Install older JDKs as necessary, like 5u18 in c:\install\jdk\sun\5u18, but don't install the public JREs.

When in development, I have a little batch file that I use to setup a command prompt for each JDK version. Essentially just set JAVA_HOME=c:\jdk\sun\JDK_DESIRED and then set PATH=%JAVA_HOME%\bin;%PATH%. This will put the desired JDK first in the path and any secondary tools like Ant or Maven can use the JAVA_HOME variable.

The path is important because most public JRE installs put a linked executable at c:\WINDOWS\System32\java.exe, which usually overrides most other settings.

I have patched the behaviour of my eclipse startup shortcut in the properties dialogue

from

"E:\Program Files\eclipse\eclipse.exe"

to

"E:\Program Files\eclipse\eclipse.exe" -vm "E:\Program Files\Java\jdk1.6.0_30\bin"

as described in the Eclipse documentation

It is a patch only, as it depends on the shortcut to fix things...

The alternative is to set the parameter permanently in the eclipse initialisation file.

I just had that problem (Java 1.8 vs. Java 9 on Windows 7) and my findings are:

short version

default seems to be (because of Path entry)

c:\ProgramData\Oracle\Java\javapath\java -version

select the version you want (test, use tab completing in cmd, not sure what those numbers represent), I had 2 options, see longer version for details

c:\ProgramData\Oracle\Java\javapath_target_[tab]

remove junction/link and link to your version (the one ending with 181743567 in my case for Java 8)

rmdir javapathmklink /D javapath javapath_target_181743567

longer version:

Reinstall Java 1.8 after Java 9 didn't work. The sequence of installations was jdk1.8.0_74, jdk-9.0.4 and attempt to make Java 8 default with jdk1.8.0_162...

After jdk1.8.0_162 installation I still have

java -versionjava version "9.0.4"Java(TM) SE Runtime Environment (build 9.0.4+11)Java HotSpot(TM) 64-Bit Server VM (build 9.0.4+11, mixed mode)

What I see in path is

Path=...;C:\ProgramData\Oracle\Java\javapath;...

So I checked what is that and I found it is a junction (link)

c:\ProgramData\Oracle\Java>dir Volume in drive C is OSDisk Volume Serial Number is DA2F-C2CC Directory of c:\ProgramData\Oracle\Java2018-02-07  17:06    <DIR>          .2018-02-07  17:06    <DIR>          ..2018-02-08  17:08    <DIR>          .oracle_jre_usage2017-08-22  11:04    <DIR>          installcache2018-02-08  17:08    <DIR>          installcache_x642018-02-07  17:06    <JUNCTION>     javapath [C:\ProgramData\Oracle\Java\javapath_target_185258831]2018-02-07  17:06    <DIR>          javapath_target_1817435672018-02-07  17:06    <DIR>          javapath_target_185258831

Those hashes doesn't ring a bell, but when I checked

c:\ProgramData\Oracle\Java\javapath_target_181743567>.\java -versionjava version "1.8.0_162"Java(TM) SE Runtime Environment (build 1.8.0_162-b12)Java HotSpot(TM) 64-Bit Server VM (build 25.162-b12, mixed mode)c:\ProgramData\Oracle\Java\javapath_target_185258831>.\java -versionjava version "9.0.4"Java(TM) SE Runtime Environment (build 9.0.4+11)Java HotSpot(TM) 64-Bit Server VM (build 9.0.4+11, mixed mode)

so to make Java 8 default again I had to delete the link as described here

rmdir javapath

and recreate with Java I wanted

mklink /D javapath javapath_target_181743567

tested:

c:\ProgramData\Oracle\Java>java -versionjava version "1.8.0_162"Java(TM) SE Runtime Environment (build 1.8.0_162-b12)Java HotSpot(TM) 64-Bit Server VM (build 25.162-b12, mixed mode)

** update (Java 10) **

With Java 10 it is similar, only javapath is in c:\Program Files (x86)\Common Files\Oracle\Java\ which is strange as I installed 64-bit IMHO

.\java -versionjava version "10.0.2" 2018-07-17Java(TM) SE Runtime Environment 18.3 (build 10.0.2+13)Java HotSpot(TM) 64-Bit Server VM 18.3 (build 10.0.2+13, mixed mode)