正则表达式查找同一字符在Java中是否重复3次或更多次

Question

My requirement is to use only Java regular expression to check if a given string contains the same character repeated more than 3 times in continuation within the string.

For ex :

"hello"  -> false
"ohhhhh" -> true
"whatsuppp" -> true

Answer 1

You can use the following regex for your problem:

^.*(.)\1\1.*$

Explanation

1. ^ starting point of your string
2. .* any char 0 to N times
3. (.) one char in the capturing group that will be used by the backreference
4. \\1 back reference to the captured character (we call it twice to force your 3 times repetition constraint)
5. .* any char 0 to N times
6. $ end of the input string

I have tested on :

hello -> false
ohhhhh -> true
whatsuppp -> true
aaa -> true
aaahhhahj -> true
abcdef -> false
abceeedef -> true

Last but not least, you have to add a backslash \\ before each backslash \\ in your regex before being able to use it in your Java code.

This give you the following prototype Java code:

  ArrayList <String> strVector = new ArrayList<String>();
  strVector.add("hello");
  strVector.add("ohhhhh");
  strVector.add("whatsuppp");
  strVector.add("aaa");
  strVector.add("aaahhhahj");
  strVector.add("abcdef");
  strVector.add("abceeedef");

  Pattern pattern = Pattern.compile("^.*(.)\\1\\1.*$");
  Matcher matcher;        

  for(String elem:strVector)
  {
    System.out.println(elem);
    matcher = pattern.matcher(elem);
    if (matcher.find())System.out.println("Found you!");
    else System.out.println("Not Found!");
  }

giving at execution the following output:

hello
Not Found!
ohhhhh
Found you!
whatsuppp
Found you!
aaa
Found you!
aaahhhahj
Found you!
abcdef
Not Found!
abceeedef
Found you!