Question

I would like to match by regex strings of 01 which have odd length.
Example: "0","001","111","11111" etc.

The idea is the odd length sequences are 0 or 1 followed by pairs of 0 or 1. But my regex seems not working.
I made this:

String regex = "[0-1]{1}[[0-1]{2}]{0,}";
    String txt = "01";
    Pattern p = Pattern.compile(regex);
    Matcher m = p.matcher(txt);

        System.out.println(m.matches());

Answer 1

Try this:

String regex = "[01]([01][01])*";
"00011".matches(regex) => true
"0001".matches(regex) => false