BEWARE that this is not recommended on endorsed in any way and you are doing so on your own risk.
First thing to notice - after upgrade all java installations you had previously are gone. OOTB some version of Java 8 is installed, but it's old so go ahead and upgrade it anyway.
IF you want, you might also go and download latest JDK 1.7 from Oracle or even JDK 1.6 from developer.apple.com. They both still work fine.
whether you use 2 or 3 doesn't matter. You might run into following error:
What it means in short is that your certificate store in JDK -
cacerts is screwed up. For me that happened w/ JDK 1.6 ... after verifying that one in JDK 1.7 is fine i just decided to use the same for both JDK versions:
You end up with Apple's compilation of 1.9.0 whatever you had before. Beware that this one will cause issues when releasing. There is workaround suggested for that on Release process page, but that works only from 1.9.2 up, so go ahead an upgrade your git too.
Seems to work fine. The only quirk I found so far is that on stack overflow, the JS in top bar doesn't work anymore (while it still works fine in Chrome and FF).