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Do I need to restart my system after setting JAVA in system environment's path variable?

I did the following steps but java does not seem to be working for me, do I need to restart my system if yes then why?
1. Right click My Computer->Advence Option->Environment Varibles->System Variables
2. variable : Path->Edit
3. Copy your jdk bin directory i.e.C:\Program Files\Java\jdk1.7.0_51\bin
4. Paste it after putting a semi-colon(;) in value section
i am getting below error while running java in cmd
C:\Users\User>java -version
Error: opening registry key 'Software\JavaSoft\Java Runtime Environment'
Error: could not find java.dll
Error: Could not find Java SE Runtime Environment.

No, but you will need to close and recreate any cmd windows, running java programs, or the like.
To check it's correct, open a new cmd window and type set -> review the information for PATH and JAVA_HOME.

You should set two things:
JAVA_HOME
PATH
The first lies under the "User variables for [your user name]" section. Add the JAVA_HOME variable and set it to where your jdk is installed. i.e. C:\Program Files\Java\jdk1.7.0_51\
The second lies under the "System variables" section. You should find the "path" variable, and edit it. Then, append ";%JAVA_HOME%\bin" (minus the quotes) to the end of the path variable.
After you have done this, save the variables and close that window clicking the "ok" button. Close down all instances of the command prompt (and any IDE you may be developing with such as Eclipse or NetBeans), and reopen one command prompt. Then, if you would like to test whether or not your changes worked and are in effect, try the following:
echo %JAVA_HOME%
This should output where you set your java home variable to.
echo %PATH%
At the end of what is output, you should see your java home\bin addition to the path variable
java -version
If you can run this command from the command line, it means that your environment was set up correctly and java is now in your path.

Not necessary. Quit and Open the command prompt again (if any) that runs the java process and type java -version to check if it installed successfully.
If you are using mac, source ~/.bashrc or source ~/.zshrc should refresh your environmental variable. No need to re-start the terminal even.

No, you don't need to restart your system.
However, you have to restart your command prompt application to update the changes done on Environment variables.

NO.
You don't need to restart the system, but just the application like cmd or any IDE you are using for java development (i.e Eclipse) need to restart.
And to confirm that the java path is set that you have mentioned in JAVA_HOME environment variable, you can open cmd and you can check with commands echo %JAVA_HOME% or echo %PATH%.

I reinstall the JDK and set the JAVA_HOME and PATH variable again. now it's working.

In my case under user variable section(for particularuser) JAVA_HOME set to jre not jdk path . I change it to JDK path , It worked for me

yes need to restart cmd prompt after env variable change

mvn --version not working?

I have problem with MAVEN path
i have already set all the path but not working please see the below path
Path
....;C:\Program Files\Java\jdk1.6.0_20\bin;D:\apache-maven-3.2.1\bin
JAVA_HOME
C:\Program Files\Java\jdk1.6.0_20
MAVEN_HOME
D:\apache-maven-3.2.1
When i try to run mvn --version it will give error of JAVA_HOME please see the error
Error: JAVA_HOME is set to an invalid directory.
JAVA_HOME = "C:\Program Files\Java\jdk1.6.0_20\bin"
Please set the JAVA_HOME variable in your environment to match the
location of your Java installation.
But javac is working fine

JAVA_HOME needs to point to the folder which contains bin/, lib/, etc.
Your variable points inside of Java's home folder.

Change JAVA_HOME C:\Program Files\Java\jdk1.6.0_20\bin to C:\Program Files\Java\jdk1.6.0_20.
PATH and JAVA_HOME are two different things:
With PATH you tell the system where to search for commands. There you should have
PATH=...;C:\Program Files\Java\jdk1.6.0_20\bin;
With JAVA_HOME you define where your Java has been installed. Applications using JAVA_HOME add the bin and/or lib directories. There you should have
JAVA_HOME=C:\Program Files\Java\jdk1.6.0_20
Try the following in a DOS-Box:
set JAVA_HOME=C:\Program Files\Java\jdk1.6.0_20
set MAVEN_HOME=D:\apache-maven-3.2.1
set PATH=%JAVA_HOME%\bin;%MAVEN_HOME%\bin
mvn --version

Once you have identified the JRE installation path:
Right-click the My Computer icon on your desktop and select Properties.
Click the Advanced tab.
Click the Environment Variables button.
Under System Variables, click New.
Enter the variable name as JAVA_HOME.
Enter the variable value as the installation path for the Java Development Kit.
If your Java installation directory has a space in its path name, you should use the shortened path name (e.g. C:\Progra~1\Java\jre6) in the environment variable instead.
Icon
Note for Windows users on 64-bit systems
Progra~1 = 'Program Files'
Progra~2 = 'Program Files(x86)'
Click OK.
Click Apply Changes.
Close any command window which was open before you made these changes, and open a new command window. There is no way to reload environment variables from an active command prompt. If the changes do not take effect even after reopening the command window, restart Windows.
If you are running the Confluence EAR/WAR distribution, rather than the regular Confluence distribution, you may need to restart your application server.

You required to set or make sure about 3 variables environment behaviour:
1. M2_HOME: set this environment variable to point out to apache maven directory. Note: must not be point to bin directory.
JAVA_HOME: This environment variable must be point to jdk folder, not include bin directory.
path: your system/user path variable must be pointing to bin directory of java environment.
this works fine for me.

first set all these things
set JAVA_HOME=C:\Program Files\Java\jdk1.6.0_20
set MAVEN_HOME=D:\apache-maven-3.2.1
set PATH=%JAVA_HOME%\bin;%MAVEN_HOME%\bin
check
mvn --version
if still not working then delete path in environment variables again create it as
PATH=%JAVA_HOME%\bin;%MAVEN_HOME%\bin
close previously opened cmd prompt
open new cmd
and check
mvn --version

Environment Variable Not recognised

I am setting Environment Variable, Still OS cant recognise. Check this out you will get it.
https://www.dropbox.com/s/raqr4wbtoxxz0b8/1.JPG
I tried with Admin privileges also still same but when I enter
echo %java_home%
or
echo %jre_home%
It is showing path corretly. Why isnt javac command working.
Any Help will be appreciated.

You don't have javac in your path. Setting the JAVA_HOME and/or JRE_HOME environment variables (which aren't needed any more, for the most part) does nothing to the PATH which the command shell uses to find executables.
Put the relevant JDK bin directory in your PATH environment variable instead - and unless you actually need JRE_HOME and JAVA_HOME for some reason, I'd get rid of them. If you do need them, get rid of the "bin" part - it should just be the root JRE directory, e.g.
c:\Program Files\Java\jdk1.7.0_45

Your path JAVA_HOME should be, for example
C:\Program Files\Java\jdk.1.7.0_45
And your Path variable should be
...;%JAVA_HOME%\bin
javac is in the bin folder which should be on your path.

That has nothing to do with Java environment variables.
When you type javac, or any other command, Windows will search the folders in the %PATH% environment variable to find an EXE file with that name.
You need to add your JDK directory to %PATH%.
You also need to restart cmd to pick up the changes.

Include the JRE/JDK path in System variables->PATH as well
After adding path varaibles,restart the cmd

You must restart cmd for new variables to be picked up. And java bin folder needs to be included in path. When you type javac it goes through all folders defined in path to find it.

JAVA_HOME error while 'play run' on Windows -- play framework

I am getting error while doing 'play run'
"Could not execute the Java executable, please make sure the JAVA_HOME environment variable is set properly (the Java executable should reside at JAVA_HOME/bin/java)."
But I can confirm that , JAVA_HOME is set correctly, as I am able to run 'java' command from console i.e. DOS prompt.
Can anyone please guide me on this?

Set user variable
JAVA_HOME to C:\Progra~1\Java\jdk1.7.0_04
and
extend the system variable
Path with %JAVA_HOME%\bin;
works for me

I had the same problem on Windows 7. echo %JAVA_HOME% returned C:\Programmes\Java\jdk1.7.0, which seemed correct. However, in Windows 7, even though path looks like that in explorer, the "real" path to use with cmd is C:\Program Files\Java\jdk1.7.0.
I updated JAVA_HOME and restarted cmd — otherwise, the terminal wouldn't refresh its variables — and it worked smoothly.

Being able to run java from your command line does NOT indicate that you have set the JAVA_HOME variable. Do you know how to do that?? Or do you know how to check if this variable exist?
Here is a quick way IF you are using Windows: Right click My Computer (or Computer in Windows 7) then click the tab Advanced then environment variables. In the System variables check if there is an entry with the variable JAVA_HOME. If NOT create one (by clicking new) giving JAVA_HOME in variable name and the path of your jdk in the variable value. IF let's say, your jdk is installed on the following path: c:\jdk6 in your pc THEN this should be your variable value. Click Ok, Ok again and then run your app again!

Have you done echo %JAVA_HOME%?
Several issues:
JAVA_HOME (a variable used by the JVM) is not the same than PATH (a variable used by the OS to locate directories where to find executables). Doing java.exe just shows that the bin directory of Java is in PATH, not that JAVA_HOME points where it should (or even it exists)
Also, Windows usually does not use the PATH variable, but instead treats java specially and stores its location in the register (do an echo %PATH% to check this).
In conclussion: You cannot assume JAVA_HOME is set; check for it directly and set it (Control Panel-> System -> Advanced).

Make sure you use a DOS-Path in JAVA-Home. Meaning no fakes from Win-7 C:\Programme in real C:\Program Files and no blank in path.
C:\>dir /x Prog*
09.08.2011 13:55 <DIR> PROGRA~1 Program Files
21.08.2011 20:25 <DIR> PROGRA~2 Program Files (x86)
This is a safe solution.
echo %JAVA_HOME% is indeed always a good idea to.

If you have a 64 bit Windows version, make sure you have both the 32bit and 64bit version of Java installed (so there must be a Java directory in both Program Files and Program Files (x86). That was my problem.

I updated my jdk from 1.6.0_14 to 1.7.0_10 and my jre6 to jre7 and had the same problem on XP.
I then deleted JAVA_HOME and added it again and it worked.
I also added JRE_HOME as a System Variable
JAVA_HOME --> C:\Program Files\Java\jdk1.7.0_10
JRE_HOME --> C:\Program Files\Java\jre7

Change where Java looks for javac.exe

I am trying to upload my GAE app using the console in windows. I am getting the error:
cannot find javac executable based on java.home tried, "C:\Program Files\Java\jre6\bin\javac.exe" and "C:\Program Files\Java\bi
n\javac.exe"
Unable to upload app: cannot find javac executable based on java.home, tried "C:
\Program Files\Java\jre6\bin\javac.exe" and "C:\Program Files\Java\bin\javac.exe
javac.exe is located in C:\Program Files\Java\jdk1.6.0_18\bin how do I tell java thats where it is

You must set the JAVA_HOME environment variable to refer to the top-level folder where java is installed. Right-click "My Computer", Properties, Advanced, Environment Variables. If there's an existing JAVA_HOME variable, then correct it so that its value is
C:\Program Files\Java\jdk1.6.0_18
If there is no existing variable, then create one by using the "New" button. It's up to you whether to do it for the current user or for the system.

Do you have two java versions installed?
From the information the sun jre and the Open jdk? The jre has no javac.exe and therefore cant find it.
Try to start your jar with C:\Program Files\Java\jdk1.6.0_18\bin\java.exe instead of only java, if that doesn't help add the -Djava.home="C:\Program Files\Java\jdk1.6.0_18" option to the call.

The error message makes it clear that the lookup is based on java.home, have you tried adjusting that?
This output looks like it is coming from some sort of script which may have it's own definition of java.home which you need to change.

The easiest solution for this problem which I found is to use the JAVA_HOME variable in the script file.
This is the content of my bin\appcfg.cmd:
#"%JAVA_HOME%"\bin\java -cp "%~dp0\..\lib\appengine-tools-api.jar" com.google.appengine.tools.admin.AppCfg %*
Note: you should also check if JAVA_HOME points to an existing JDK

The other way you can do set classpath variable using set CLASSPATH=C:\Program Files\Java\jre6\bin\javac.exe\jdk1.6.0_18 in command prompt, but it works for single session.Everytime you need to set the variable.

Set your JAVA_HOME environment variable to C:\Program Files\Java\jdk1.6.0_18. Note that this variable points to the JDK location, not (unlike the PATH environment variable) to the path where the executables reside.