The endorsed standards override mechanism and the extensions mechanism were removed in JDK 9 via JEP 220.

The CheckEndorsedAndExtDirs option is disabled by default. However, if it's enabled in the command-line, the VM would check the endorsed and ext directories so that the VM terminates if they exist. These checks are no longer needed in JDK 10 and beyond and can be removed.

This task is the first step in the removal -- we need to mark this option as deprecated and print a warning message when it's used. The option itself, and the code that uses it, will be removed in a subsequent JDK release.