Error:Execution failed for task ':app:javaPreCompileDebug'.
> Annotation processors must be explicitly declared now.  The following dependencies on the compile classpath are found to contain annotation processor.  Please add them to the annotationProcessor configuration.
    - butterknife-6.0.0.jar (com.jakewharton:butterknife:6.0.0)
  Alternatively, set android.defaultConfig.javaCompileOptions.annotationProcessorOptions.includeCompileClasspath = true to continue with previous behavior.  Note that this option is deprecated and will be removed in the future.
  See https://developer.android.com/r/tools/annotation-processor-error-message.html for more details.

在app的build中

android {
    ...
    defaultConfig {
        ...
        //添加如下配置就OK了
        javaCompileOptions { annotationProcessorOptions { includeCompileClasspath = true } }
    }
    ...
}