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上没有这个问题，有人说jdk的问题，试了一下jdk7和jdk8都有这个问题，后来查到原因是和gradle最新的插件不兼容，改成1.5.0之后解决！
classpath 'com.android.tools.build:gradle:1.5.0'
将2.1换成1.5就好了。
android studio真坑爹！