Mac OS X 10.10 doesn't fit the JDK's install version check. Can't install java on the beta I assume...
This is a know issue and is being addressed. Here is the bug report https://bugs.openjdk.java.net/browse/JDK-8027686
When builds of 8u20 and 7u60 that have the fix are made available, you can find them here:
A build with the fix has been posted here: https://jdk8.java.net/download.html