Doesn't work macros for environment variables in Windows 7 - windows

Question

I have set JAVA_HOME variable
And also I have set path variable:
C:\>set java_home
JAVA_HOME=C:\Program Files\Java\jdk1.6.0_38
C:\>set path
Path=C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32\Wbem;C:\WINDOWS\System32\WindowsPowerShell\v1.0\;C:\Program Files\To
rtoiseSVN\bin;%JAVA_HOME%\bin;C:\Program Files\apach\apache-maven-3.2.3\bin
PATHEXT=.COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC
C:\>java -version
'java' is not recognized as an internal or external command,
operable program or batch file.
C:\>
At this way java is not recognized.
Lets change a bit(replace %JAVA_HOME%\bin with C:\Program Files\Java\jdk1.6.0_38\bin):
C:\>set java_home
JAVA_HOME=C:\Program Files\Java\jdk1.6.0_38
C:\>set path
Path=C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32\Wbem;C:\WINDOWS\System32\WindowsPowerShell\v1.0\;C:\Program Files\To
rtoiseSVN\bin;C:\Program Files\Java\jdk1.6.0_38\bin;C:\Program Files\apach\apache-maven-3.2.3\bin
PATHEXT=.COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC
C:\>java -version
java version "1.6.0_38"
Java(TM) SE Runtime Environment (build 1.6.0_38-b05)
Java HotSpot(TM) 64-Bit Server VM (build 20.13-b02, mixed mode)
For this way it is working good.
What do I wrong?

Answer 1

"%JAVA_HOME%\bin" is a perfectly valid directory name. cmd would need to evaluate its value before it could be used.
call set path=%path%
should work for you.
Expansion
path is loaded with the system value, then merged with the 'user' value, when any %var% in the path is replaced by its then-current value. If you add another %var% into the path (like for instance, as a "user" variable) then you need to re-evaluate to resolve the value.
The upshot is: set the path as a system variable, not a user variable if it contains a value to be resolved.