I had the same problem (OSX 10.10 Yosemite Beta public 2)I have a good method and it's work for me :
downloaded Java for OS X 2014-001(http://support.apple.com/downloads/DL1572/en_US/JavaForOSX2014-001.dmg).DON'T INSTALL (because, it says that already install)
download the last BETA version of JDK™ ( 8u40, at this date) https://jdk8.java.net/download.html (Choose JDK version) INSTALL IT
For the next step, install the first download : Java for OS X 2014-001 Now the program should start the installation normally
MIRACLE Minecraft launcher works now!
Guillaume Robinet
I had the same problem (OSX 10.10 Yosemite Beta public 2)
I have a good method and it's work for me :
downloaded Java for OS X 2014-001
(http://support.apple.com/downloads/DL1572/en_US/JavaForOSX2014-001.dmg).
DON'T INSTALL (because, it says that already install)
download the last BETA version of JDK™ ( 8u40, at this date)
https://jdk8.java.net/download.html (Choose JDK version)
INSTALL IT
For the next step, install the first download : Java for OS X 2014-001
Now the program should start the installation normally
MIRACLE Minecraft launcher works now!