question: static void checkInternalName ( final String name , final int start , final int end , final String msg ) { int max = end == - 1 ? name . length ( ) : end ; try { int begin = start ; int slash ; do { slash = name . indexOf ( '/' , begin + 1 ) ; if ( slash == - 1 || slash > max ) { slash = max ; } checkIdentifier ( name , begin , slash , null ) ; begin = slash + 1 ; } while ( slash != max ) ; } catch ( IllegalArgumentException unused ) { throw new IllegalArgumentException ( "Invalid " + msg + " (must be a fully qualified class name in internal form): " + name ) ; } }
target:  Checks that the given substring is a valid internal class name.