String: How to replace multiple possible characters with a single character?

Question

I would like to replace all \'.\' and \' \' with a \'_\'

but I don\'t like my code...

is there a more efficient way to

Answer 1

s.replaceAll("[\\s\\.]", "_")

Answer 2

String new_s = s.toLowerCase().replaceAll("[ .]", "_");

EDIT:

replaceAll is using regular expressions, and using . inside a character class [ ] just recognises a . rather than any character.

Answer 3

Use String#replace() instead of String#replaceAll(), you don't need regex for single-character replacement.

I created the following class to test what's faster, give it a try:

public class NewClass {

    static String s = "some_string with spaces _and underlines";
    static int nbrTimes = 10000000;

    public static void main(String... args) {

        long start = new Date().getTime();
        for (int i = 0; i < nbrTimes; i++)
            doOne();
        System.out.println("using replaceAll() twice: " + (new Date().getTime() - start));



        long start2 = new Date().getTime();
        for (int i = 0; i < nbrTimes; i++)
            doTwo();
        System.out.println("using replaceAll() once: " + (new Date().getTime() - start2));

        long start3 = new Date().getTime();
        for (int i = 0; i < nbrTimes; i++)
            doThree();
        System.out.println("using replace() twice: " + (new Date().getTime() - start3));

    }

    static void doOne() {
        String new_s = s.toLowerCase().replaceAll(" ", "_").replaceAll(".", "_");
    }

    static void doTwo() {
        String new_s2 = s.toLowerCase().replaceAll("[ .]", "_");
    }

    static void doThree() {
        String new_s3 = s.toLowerCase().replace(" ", "_").replace(".", "_");
    }
}

I get the following output:

using replaceAll() twice: 100274

using replaceAll() once: 24814

using replace() twice: 31642

Of course I haven't profiled the app for memory consumption, that might have given very different results.