Select a particular JRE from the command lineTag(s): Environment

If the JRE is properly installed on Windows, informations about each version are stored in the registry. The installation process installs a special java.exe in the system PATH. So you don't need to alter you PATH because this special java.exe will find the current JRE. From a command line, type java -version to display the current jre version installed.

With release 1.6, it's now possible to select a different JRE installation than the last one without any registry modification.

The JRE installation are listed in the registry in the key HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment

Take this simple test class

public class ShowVersion {
 public static void main(String args[]) {
   System.out.println(System.getProperty("java.version"));
 }
}

> java ShowVersion

To force the 1.5 JRE instead, use this command line.

> java -version:"1.5" ShowVersion

ref : Java 6 technotes

You can always give the complete path to use a specific installation. Launching the JVM this way does not use the registry setting at all.

>"C:\Program Files\Java\j2re1.4.1_02\bin\java" -version
java version "1.4.1_02"