Question

I have a string like foo..txt and I want to convert it to foo.txt
The occurence of ‘.’ may be more than 2 also.
What is the best way to accomplish this?

edit : The ‘.’ may not occur just together. The occurences may be as below too

foo.bar.txt = foo bar.txt
foo..bar.foo.txt = foo bar.txt

Answer 1

I believe what you want is to replace all periods in the file name part with spaces, but keep the extension, right?

If so, something like this would be appropriate:

    String[] tests = {
        "foo.bar.txt",       // [foo bar.txt]
        "foo...bar.foo.txt", // [foo bar foo.txt]
        "........",          // [.]
        "...x...dat",        // [x.dat]
        "foo..txt",          // [foo.txt]
        "mmm....yummy...txt" // [mmm yummy.txt]
    };
    for (String test : tests) {
        int k = test.lastIndexOf('.');          
        String s = test.substring(0, k).replaceAll("\\.+", " ").trim()
           + test.substring(k);
        System.out.println("[" + s + "]");
    }

Essentially the way this works is:

• First, find the lastIndexOf('.') in our string
  • Say this index is k, then we have logically separated our string into:
    • substring(0, k), the prefix part
    • substring(k), the suffix (file extension) part
• Then we use regex on the prefix part to replaceAll matches of \.+ with " "
  • That is, a literal dot \., repeated one or more times +
  • We also trim() this string to remove leading and trailing spaces
• The result we want is the transformed prefix concatenated with the original suffix

Clarifications

• The reason why the pattern is \.+ instead of .+ is because the dot . is a regex metacharacter, but in this case we really mean a literal period, so it needs to be escaped as \.
• The reason why this pattern as a Java string literal is "\\.+" is because \ is itself a Java string literal escape character. For example, the string literal "\t" contains the tab character. Analogously, the string literal "\\" contains the backslash character; it has a length() of one.

References

• regular-expressions.info/The Dot Matches (Almost) Any Character and Repetition with Star and Plus
• String API: lastIndexOf and trim()
• JLS 3.10.6 Escape Sequences for Character and String Literals