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Support for a system Java on macOS has been removed - install a fairly recent Oracle Java (see ‘R Installation and Administration’ §C.3.2).
The maximum number of DLLs that can be loaded into R e.g. _via_ ‘dyn.load()’ has been increased up to 614 when the OS limit on the number of open files allows.
‘R CMD javareconf’ has been updated to recognize the use of a Java 9 SDK on macOS.