java regular expression with replaceAll on string

Question

I have two strings :

s = "aaaaaaa" and m = "a"

I want output as commonChars="a" but i am getting commonChars="aaaaaaa" and for s = "a" m = "aaaa"

I want output commonChars="a"

Can anyone suggest me regular expression for that ?

My code is

String commonChars = s.replaceAll("[^" + m + "]", "");

Answer 1

You could do

String commonChars = s.replaceAll(m + "+", m);