Found that: if you install java8 update25, which is the newest Java update on Mac, the default JDK is 6 not 7.
official info: http://support.apple.com/kb/DL1572
But the Android studio default recommend JDK version is 7.
So you need to download the JDK7 from here:
http://www.oracle.com/technetwork/java/javase/downloads/jdk7-downloads-1880260.html
1.Open the dmg, and install.
2.In your android studio, go to File> Project Structure> SDK Location
3.In "JDK location" click on browse and go to
/Library/Java/JavaVirtualMachines/jdk1.7.0_60.jdk/Contents/Home(Note :- Its Not
/System/Library it's /Library)
4. apply, then ok!
