ANDROID STUDIO 3.0 upgrade : Error:Could not resolve all files for configuration ':app:xxxxxxxDebugCompileClasspath'
change dependency declaration
from
compile files('libs/commons-lang-2.4.jar')
to
implementation files('libs/commons-lang-2.4.jar')
I had the same problem, build -> clean project worked for me.
Change the classpath of Project Gradle to:
classpath 'com.android.tools.build:gradle:3.1.0-alpha01'
OR
change distributionUrl of gradle-wrapper.properties to
distributionUrl=https\://services.gradle.org/distributions/gradle-4.1-all.zip
Hope it helps you