@echo off
cls
setlocal ENABLEEXTENSIONS
set KEY_NAME="HKLM\SOFTWARE\JavaSoft\Java Runtime Environment"
set VALUE_NAME=CurrentVersion

::
:: get the current version
::
FOR /F "usebackq skip=4 tokens=3" %%A IN (`REG QUERY %KEY_NAME% /v %VALUE_NAME% 2^>nul`) DO (
    set ValueValue=%%A
)

if defined ValueValue (
    
    @echo the current Java runtime is  %ValueValue%
) else (
    @echo %KEY_NAME%\%VALUE_NAME% not found.
    goto end
)

set JAVA_CURRENT="HKLM\SOFTWARE\JavaSoft\Java Runtime Environment\%ValueValue%"
set JAVA_HOME=JavaHome

::
:: get the javahome
::
FOR /F "usebackq skip=4 tokens=3,4" %%A IN (`REG QUERY %JAVA_CURRENT% /v %JAVA_HOME% 2^>nul`) DO (
    set JAVA_PATH=%%A %%B
)

echo the path of the current Java JVM according to the registry is 
echo %JAVA_PATH%
echo.
echo now if we try it :
"%JAVA_PATH%\bin\java.exe" -version

:end

>j.cmd
the current Java runtime is  1.6
the path of the current Java JVM according to the registry is
C:\Program Files\Java\jre1.6.0_06

now if we try it :
java version "1.6.0_06"
Java(TM) SE Runtime Environment (build 1.6.0_06-b02)
Java HotSpot(TM) Client VM (build 10.0-b22, mixed mode, sharing)