rJava install error "JAVA_HOME cannot be determined from the Registry"
This error is often resolved by installing a Java version (i.e. 64-bit Java or 32-bit Java) that fits to the type of R version that you are using (i.e. 64-bit R or 32-bit R). This problem can easily effect Windows 7 users, since they might have installed a version of Java that is different than the version of R they are using.
Install 64 bit Java from https://java.com/en/download/manual.jsp.
Then in windows cmd runsetx PATH "C:\Program Files\Java\jre1.8.0_211\bin\server;%PATH%"
(make sure your path is correct).
Then in RStudio runSys.setenv(JAVA_HOME="")
Now, you should be able to run rJava!!
I got the same error resolved by installing same version of R and Java i.e. 64 bits and manually updating the path i.e. ,
Sys.setenv(JAVA_HOME='C:/Program Files/Java/jre1.8.0_121') # for 64-bit version