import java.util.*;
import static java.util.Comparator.*;

class Ideone {
public static void main(String[] args) {
        List<String> strings = Arrays.asList("room1.2", "foo1.1", "room2.3", "room100.999", "room10", "room.3");
        Collections.sort(strings, Comparator.comparing(Ideone::extractDouble));
        System.out.println(strings);
    }

    static double extractDouble(String s) {
        String num = s.replaceAll("[^\\d.]", "");
        // return 0 if no digits found
        return num.isEmpty() ? 0 : Double.parseDouble(num);
    }
}