Class JavaLaunchHelper is implemented in both /Library/Java/JavaVirtualMachines/jdk1.8.0_25.jdk/Contents/Home/bin/java and /Library/Java/JavaVirtualMachines/jdk1.8.0_25.jdk/Contents/Home/jre/lib/libinstrument.dylib. One of the two will be used. Which one is undefined
windows上沒有這個問題，有人說jdk的問題，試了一下jdk7和jdk8都有這個問題，后來查到原因是和gradle最新的插件不兼容，改成1.5.0之后解決！
classpath 'com.android.tools.build:gradle:1.5.0'
將2.1換成1.5就好了。
android studio真坑爹！