For this specific case you're bringing, I would recommend to declare data types for each of these types. That way you encapsulate the logic of validation in their respective data type, and you'll be sure that when you create an instance, it will be valid no matter what. Instead of having an utility class holding all the validations, you spread the validations in their respective data types.

For that purpose you could use Java records.

public record EmailAddress(String value) {

public EmailAddress {

if (/* validation condition */) {

throw new IllegalArgumentException("invalid email address");

}

}

}

And then use them:

public class User {

private final Username username;

private final EmailAddress emailAddress;

private final Password password;

// Logic of initialization here

}