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Public and Private JRE

This one is basic. Newbies in Java are overwhelmed with too many techy terms. Most know JRE, but some find it hard to understand the notation of a Public and Private JRE.

A JRE is nothing but a folder that contains JVM executables, setting files, required lib files, and extensions. You can install multiple JREs on your system Sun generally installs versions in C:\Program Files\Java as jre eg.jre1.6.0_06.

A Public JRE is available to all Java programs, Browsers, and the libs in this JRE folder are available to applications started in command line like
java com.sarathonline.cli.HelloWorld
This JRE is also registered in path, and Browser plugin.

A Private JRE is something that is installed in the system by is not refered to by default. This could be a copy of the JRE / JDK folder from another installed directory. If you see a my earlier post:  starting eclipse with jre 1.6 where your environment is in 1.4, The JRE1.6 is used only by Eclipse, This is a private JRE. While the JAVA_HOME points to 1.4. This is a public JRE.

Why do you need to know this? One situation you would face is the one I explained above. Another example: JRE is not just by Sun, there could be vendor JREs like Weblogic uses JRockit JRE. So you could notice, that a Weblogic server could be started even in a system where java is not installed. Because that is using its own private JRE.

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