Question

I have a string. How I can check if the string is a regular expression or contains regular expression or it is a normal string?

Answer 1

The only reliable check you could do is if the String is a syntactically correct regular expression:

boolean isRegex;
try {
  Pattern.compile(input);
  isRegex = true;
} catch (PatternSyntaxException e) {
  isRegex = false;
}

Note, however, that this will result in true even for strings like Hello World and I'm not a regex, because technically they are valid regular expressions.

The only cases where this will return false are strings that are not valid regular expressions, such as [unclosed character class or (unclosed group or +.