Using $ anchor inside a character class does not work

Question

I am trying to write a Regex to match a String having 1st 10 characters capital-alpha numeric and then a space and some other text or a String having 1st 10 alpha numeric charac

Answer 1

The $ symbol in [...] is treated literally. Use alternation to require either "space followed by something" or "end of line":

[A-Z0-9]{10}(?:\s.*|$)

Demo: https://regex101.com/r/f4ufzx/1

Answer 2

You don't need angular brackets for space, try below:

System.out.println("MNA345QWRE ABC".matches("[A-Z0-9]{10}(\\s|$).*"));
System.out.println("MNA345QWRE_ABC".matches("[A-Z0-9]{10}(\\s|$)*"));
System.out.println("MNA345QWRE".matches("[A-Z0-9]{10}(\\s|$).*"));