question: public Depend ( PathImpl source , long digest , boolean requireSource ) { this ( source ) ; long newDigest = source . getCrc64 ( ) ; _requireSource = requireSource ; if ( newDigest == digest ) { } else if ( ! requireSource && newDigest == 0 ) { } else if ( newDigest == 0 ) { if ( log . isLoggable ( Level . FINE ) ) log . fine ( _source . getNativePath ( ) + " source is deleted." ) ; _isDigestModified = true ; } else { _isDigestModified = true ; } }
target:  Create a new dependency with a given digest.