How regex pattern write to check at least one string and number in Java?

You could use String#matches with the following regex pattern:

^[A-Z0-9]*(?:[0-9][A-Z0-9]*[A-Z]|[A-Z][A-Z0-9]*[0-9])[A-Z0-9]*$

Sample Java code:

List<String> inputs = Arrays.asList(new String[] { "111AB", "111", "AB", "111AB$" });
for (String input : inputs) {
    if (input.matches("[A-Z0-9]*(?:[0-9][A-Z0-9]*[A-Z]|[A-Z][A-Z0-9]*[0-9])[A-Z0-9]*")) {
        System.out.println(input + " => VALID");
    }
    else {
        System.out.println(input + " => INVALID");
    }
}

This prints:

111AB => VALID
111 => INVALID
AB => INVALID
111AB$ => INVALID

Note that the regex pattern actually used with String#matches do not have leading/trailing ^/$ anchors. This is because the matches API implicitly applies the regex pattern to the entire string.

For an explanation of the regex pattern, it simply tries to match an input with has at least one digit or letter, in any order.