Well, if you know for sure that the license plate has the format "LLL NNN" (I mean letter by L and number by N), then you can get the integer value like this:

int anIntegerValue =...

public class User {

protected String userName;
protected String password;
protected String eMail;
private String aString = "I won't be inherited!!!";//It really won't

public...

Well,
static means (at least in Java, but I think it's the same) that you don't need to create an instance of that class, you can access that method directly: ClassName.methodName([params]).
void...