第一步、打开ba sh_profile环境变量，命令open .bash_profile：
第二步、修改环境变量，并source .bash_profile
export JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk11.0.1.jdk/Contents/Home
export PATH=${PATH}:$JAVA_HOME/bin:PATH
第三步、File->ProjectStructure->SDKs->+(添加并选择11)->OK
第四步、修改build.gradle中sourceCompatibility->Ok,aply suggestion!
group = 'yang.shuai'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '1.8'
成功如图所示：