question: public static boolean isExtension ( String filename , String [ ] extensions ) { if ( filename == null ) { return false ; } if ( extensions == null || extensions . length == 0 ) { return indexOfExtension ( filename ) == - 1 ; } String fileExt = getExtension ( filename ) ; for ( String extension : extensions ) { if ( fileExt . equals ( extension ) ) { return true ; } } return false ; }
target:  Checks whether the extension of the filename is one of those specified. <p> This method obtains the extension as the textual part of the filename after the last dot. There must be no directory separator after the dot. The extension check is case-sensitive on all platforms.