Goal

Provide a mechanism to override certain classes included in J2SE platform.

Reason

Those endorsed standards are defined through processes other than JCP. In other words these standards are not under the control of JCP, such as w3c and OMG. So these standards may subject to change between releases of Java2 platform. Such a mechanism can let developers and software vendors to take advantage of new revisions to endorsed standards.

Means

If JVM can find certain classes in a special directory called endorsed dir, these classes definition will override those included in J2SE platform. The default endorsed dir locates in <java-home>\lib\endorsed [Microsoft Windows] or <java-home>/lib/endorsed [Solaris or Linux]

Here <java-home> refers to the directory where the runtime software is installed (which is the top-level directory of the Java 2 Runtime Environment or the jre directory in the Java 2 SDK).

You can change the default location to another locations, however, by setting a JVM option called java.endorsed.dirs. Separate multiple directories with File.pathSeparatorChar.

Scope

Obviously, not all platform classes can be overridden. Classes can be overridden are listed on the page of http://java./j2se/1.4.2/docs/guide/standards/.