question: private static String doGetPath ( String filename , int separatorAdd ) { if ( filename == null ) { return null ; } int prefix = getPrefixLength ( filename ) ; if ( prefix < 0 ) { return null ; } int index = indexOfLastSeparator ( filename ) ; int endIndex = index + separatorAdd ; if ( prefix >= filename . length ( ) || index < 0 || prefix >= endIndex ) { return "" ; } return filename . substring ( prefix , endIndex ) ; }
target:  Does the work of getting the path.