Develop Reference

Where does Windows keep JDK location reference?

I previously had Java 7 installed on my Windows PC. System environment variable also had location to it. I installed Java 10 without uninstalling 7 or changing the environment variable. Now when I go to CMD or Cygwin and enter Java -version it says Java 10.
I would think since I didn't change the environment variable that it would still be 7. How is Windows deciding what JDK to use?
Thanks!

Probably your JAVA_HOME or just PATH environment variables were changed.
Go to command line and do the following to check it:
> echo %JAVA_HOME%
For example, for me it gives back:
C:\Program Files\Java\jdk-9.0.4

How is Windows deciding what JDK to use?
Windows is NOT making decisions on its own. If you get version 10 information when you run java -version, it is because Windows is finding the folder containing java.exe corresponding to the version 10 first in the paths pointed to by the PATH environment variable. If you have installed Java using an installer, the installer would update the PATH variable for you. Check your PATH variable and you will see the Java 10 folder appearing there first and then Java 7 folder.

If you are using a java ide , you might find the location in JRE configurations. for example in eclipse :
windows > preferences > Installed JREs
.

Your JAVA_HOME variable might still be set to JDK 7 directory, however the Java 10 installation may have inserted it's /bin directory to the PATH.
Check to ensure that java 10 isn't on the PATH before java 7, or hasn't overwritten it.
CMD etc. check the path for the binaries for commands like java-version.

Unsupported Java Version: Cannot start under Java 1.7: Java 1.8 or later is required

I just updated to IntelliJ IDEA 16 which comes with Java JDK 1.8. Fyi, I had downloaded Java JDK 1.8 a long time ago.
I tried to run my plugin that I am developing, and I cannot even do that, I get the following error message (slightly condensed)
"C:\Program Files\Java\jdk1.7.0_45\bin\java" -Xmx512m -Xms256m -XX:MaxPermSize=250m -ea "-Xbootclasspath/a:C:/Program Files (x86)/JetBrains/IntelliJ IDEA Community Edition 144.3143.6\lib\boot.jar" -Didea.config.path=C:\Users\Christopher.IdeaIC14\system\plugins-sandbox\config - ... -Dfile.encoding=windows-1252 -classpath "C:\Program Files\Java\jdk1.7.0_45\lib\tools.jar; ... ;C:\Program Files (x86)\JetBrains\IntelliJ IDEA Community Edition 144.3143.6\lib\idea_rt.jar" com.intellij.rt.execution.application.AppMain com.intellij.idea.Main
Unsupported Java Version: Cannot start under Java 1.7.0_45-b18: Java 1.8 or later is required.
So, I clearly know what the problem is; however, I cannot seem to figure out where the location to fix this is.
I have tried a lot of things so far; most involve using the search box in Settings and switching whatever I could to version 1.8. Also, I had updated my Environment Variable for Java from 1.6 to 1.8
With all of these changes, nothing is working! So how do I go about fixing this seemingly simple issue?

Set IDEA_JDK (or IDEA_JDK_64) environment variable.
Check Selecting the JDK version the IDE will run under

TL;DR --> Set JAVA_HOME to C:\Program Files\Java\jdk1.8.0_51
Java 8 is required to run IntelliJ IDEA starting from version 16 on all the supported platforms.
The actual JDK version used by the IDE can be verified in Help | About dialog (open any project to access the menu).
idea64.exe uses this JDK search in the following sequence:
IDEA_JDK_64 environment variable
..\jre64 directory
system Registry
JDK_HOME environment variable
JAVA_HOME environment variable

Under Arch Linux you can simply set java 8 as default (you must have it installed):
$ sudo archlinux-java set java-8-openjdk

In case anyone arrives here and hasn't had any luck with the other solutions, try this. I'm using PhpStorm under OSX, but the steps are probably applicable to JetBrains' other IDEs too:
Navigate to your IDE's config folder (see this article to learn how to find this folder's location).
Open the idea.propeties file.
If a JVMVersion attribute exists, delete that entire entry. If it doesn't exist, then this probably won't be of much help!
Save the file.
Launch your IDE.

Just set JAVA_HOME system variable to your JDK 8:

Run in cmd
setx JAVA_HOME "C:\Program Files\Java\jdk1.8.0_111"
don't foget to change to your java path

In my case, Ubuntu 14 (32-bit), I opened the file:
/home/<user>/Programs/PhpStorm/bin/phpstorm.sh
and after
if [ "$JDK" = "" ] && [ "$OS_TYPE" = "Linux" ] && ........... fi
I added:
if [ "$JDK" = "" ]; then
JDK="/usr/lib/jvm/java-8-oracle"
fi
And then it works!

Double check that your JAVA_HOME points to the correct 1.8 Installation and make sure that in the PATH env there is no reference to "C:\Program Files\Java\jdk1.7.0_45\bin".
Try to print your JAVA_HOME/PATH from the Console and see what the output is. If your changes are not reflected logout and then login again.

IntelliJ 16 REQUIRES Java 8 to run, it won't run under Java 7. It's compiled to Java 8 classes so it can't ever be run on an older JVM.
This is well and clearly mentioned in the documentation.
So if you have your system JVM be an older one, it will fail to start unless you coerce it into using a non-default JVM.
Possibly you have some java related executables left over in your Windows/System32 directory, where some older Java installers would drop them. Delete these by hand from the file system and see what happens.

Just in case this page needs one more recommendation, I fixed the problem in my case by going to the IDE's config folder (as #Nate puts it, see here for how to locate it), and deleting the idea.jdk file (which held a reference to a 1.6 VM).

Apart from setting the correct Java version for the global, per project and per module SDK, for the Java Compiler, and for the language level, you also must set the Target bytecode version both for the project and (if you use maven) for each maven module.
Often the project bytecode version is correct but the module bytecode version is lower, i.e. 1.5.
The per-module bytecode version is not displayed when opening the default preferences via File > Other Settings > Default Settings. You must edit the current preferences either via a shortcut (i.e. ⌘+,) or from the main menu as shown below (for mac):

I had the same problem. All paths pointing to java jdk 8, but still throwing the error. I was able to run Android Studio by running the "studio64.exe" instead "studio.exe" in the bin folder

JAVA_HOME and java -version

I'm using a Windows .bat script and I set JAVA_HOME as C:/Program Files/Java/jdk1.6.0_32
when I do a java -version, it still shows the 1.3
How can I fix this? What am I doing wrong?

For me the issue was in my PATH variable, C:\ProgramData\Oracle\Java\javapath; was added by java windows install before my %JAVA_HOME%\bin;.
So I'd echo %JAVA_HOME% pointing to a JDK7 and java -version showing jdk8.
I'd to put %JAVA_HOME%\bin; before C:\ProgramData\Oracle\Java\javapath; so that java -version displays jdk7.

Try %JAVA_HOME%\bin\java -version
If you modify JAVA_HOME, it's usually better to invoke java with an absolute path (using JAVA_HOME) because the new binary is probably not in the path (and then Windows will load the wrong binary).

Make sure that the PATH environment variable is pointing to %JAVA_HOME%\bin.

Be sure not to mix the system variable path and the user variable system path. I feel OK in calling java without the absolute path (when I know how JAVA_HOME and PATH are configured).

Calling java -version from command line, causes cmd.exe to do the lookup on the "known" directories. "Known" means PATH environment variable. It seems that your PATH contains a java 1.3 bin folder, and not 1.6.
JAVA_HOME is another variable, that is used (for example, and not only) by java wrappers, or by scripts executing some java stuff.
Try doing this:
SET JAVA_HOME=C:/Program Files/Java/jdk1.6.0_32
%JAVA_HOME%/bin/java -version
Add quotes where needed.

I had similar issue,in my case , I had two versions java installed. it can be fixed by uninstalling one version of java completely from system.

Had a similar scenario today - two Windows 10 devices - both have JRE 1.6 & 1.7.
When typing
Java -version
One device shows 1.6 the other 1.7.
This was preventing me running a third party JAR to install some software on the device showing 1.6 (which worked fine on the device showing 1.7 when running java -version), using:
java -jar ThirdParty.jar
As the JAR needed to be run by 1.7.
Cause of this was in the PATH environment variable - one device had the location of 1.6 first in the PATH list, moving the 1.7 location above the 1.6 location resulted in consistency using Java -version and allowed me to install the software.

java -version will consult the paths in the special environment variable Path. You need to select the java version you want and move it upwards the latter (click "Move Up"). You probably have that reference to JDK 1.3 in Path above your addition of JDK 1.6. Since that's the first thing the OS finds, that's what it chooses to run.
Executing the command again with the same window opened after changing the environment variables will not work. Re-open it
I know this question is old but this was my case and I wanted to re-explain further, similar to #DanBot 's case

jdk installer for windows 7 does not set path

It seems the JDK installer on Windows 7 does not install a path variable to find javac. I can set it manually. But I do not like to change it with any new update of JDK. Does it use any other environment variable? Or is it really that weird?

I don't know of a JDK installer which sets the PATH on any system.
You can install several version of the JDK and if you use an IDE, you don't need to set the path. If you want to use javac manually (don't ask me why you would) you need to set the PATH to specific which version to use.

Yes You can using environment variables. Which available in Control panel -> system

What is JAVA_HOME? How does the JVM find the javac path stored in JAVA_HOME?

I would like to know what JAVA_HOME is. Where do I set the path of javac.exe and java.exe. It is in environment variables? When I compile a Java program from command prompt, how does the JVM find javac.exe?

JVM does not find java.exe. It doesn't even call it. java.exe is called by the operating system (Windows in this case).
JAVA_HOME is just a convention, usually used by Tomcat, other Java EE app servers and build tools such as Gradle to find where Java lives.
The important thing from your point of view is that the Java /bin directory be on your PATH so Windows can find the .exe tools that ship with the JDK: javac.exe, java.exe, jar.exe, etc.

JAVA_HOME and JRE_HOME are not used by Java itself. Some third-party programs (for example Apache Tomcat) expect one of these environment variables to be set to the installation directory of the JDK or JRE. If you are not using software that requires them, you do not need to set JAVA_HOME and JRE_HOME.
PATH is an environment variable used by the operating system (Windows, Mac OS X, Linux) where it will look for native executable programs to run. You should add the bin subdirectory of your JDK installation directory to the PATH, so that you can use the javac and java commands and other JDK tools in a command prompt window. Courtesy: coderanch

set environment variable
JAVA_HOME=C:\Program Files\Java\jdk1.6.0_24
classpath=C:\Program Files\Java\jdk1.6.0_24\lib\tools.jar
path=C:\Program Files\Java\jdk1.6.0_24\bin

The command prompt wouldn't use JAVA_HOME to find javac.exe, it would use PATH.

JAVA_HOME is a environment variable (in Unix terminologies), or a PATH variable (in Windows terminology). A lot of well behaving Java applications (which need the JDK/JRE) to run, looks up the JAVA_HOME variable for the location where the Java compiler/interpreter may be found.

JAVA HOME is used for setting up the environment variable for JAVA. It means that you are providing a path for compiling a JAVA program and also running the same. So, if you do not set the JAVA HOME( PATH ) and try to run a java or any dependent program in the command prompt.
You will deal with an error as
javac : not recognized as internal or external command.
Now to set this, Just open your Java jdk then open bin folder then copy the PATH of that bin folder.
Now, go to My computer right click on it----> select properties-----> select Advanced system settings----->Click on Environment Variables------>select New----->give a name in the text box Variable Name and then paste the path in Value.
That's All!!

JAVA_HOME is an environment variable which is read by some development tools like Apache Tomcat, Apache Maven, Gradle, Jenkins etc. Usually, JAVA_HOME is set to point to JDK instead of JRE because these development tools need to use tools like compiler, debugger, document generator etc. which are only available in JDK since JDK is a development kit. JRE is only meant for running java applications. JDK = JRE + Development tools
Consumer facing Java applications don't read JAVA_HOME variable and they just need to know where the JVM is located and that's why JVM location (directory) needs to be added to the PATH variable. This is automatically done for you when you install Java software. Whenever you try to run a Java application by either double clicking on the app or through command line, your operating system reads PATH variable to locate and run JVM and it doesn't look for JAVA_HOME variable.

use this command /usr/libexec/java_home to check the JAVA_HOME

JAVA_HOME is an Environment Variable set to the location of the Java directory on your computer.
PATH is an internal DOS command that finds the /bin directory of the version of Java that you are using. Usually they are the same, except that the PATH entry ends with /bin

Basically JAVA_HOME is use to set path of the java . it is use in windows. it's used for set path of the multiple software like as java EE , ANT and Maven.
this is the steps to solve your problem:
only for core java to set path :
path :"C:\Program Files\Java\jre1.8.0_77\bin"
but when you are use multi built like as ANT , core java then you are used JAVE_HOME in environment .
follow the steps :
JAVA_HOME:"C:\Program Files\Java\jre1.8.0_77\bin"
ANT_HOME:"C:\ant\apache-ant-1.9.6"
Path: JAVA_HOME, ANT_HOME;
it is the systematic way to set the environment variable..