In java, without Arrays and using only String methods

// Question 17: In MS-DOS, a file name consists of up

// to 8 characters (excluding '.', ':', backslask, '?',

// and '*'), followed by an optional dot ('.' character)

// and extension. The extension may contain zero to three

// characters. For example, 1STFILE.TXT is a valid filename.

// Filenames are case-blind.

//

// Write and test a method that takes

// in a String, validates it as a valid MS-DOS file

// name, appends the extensions ".TXT" if no extension

// is given (that is, no '.' appears in FILENAME), converts

// the name to uppercase, and returns the resulting string

// to the calling method

// If fileName ends with a dot, remove that dot and do not

// append the default extension. If the name is invalid,

// validFileName should return null.

public String validFileName(String n)

{

}