如何找到超类 object 的子类？ （爪哇）

Question

I'm writing a library management system. For the login process, I have a log (implemented via ArrayList ) that contains objects of type, User . User is a superclass for the subtypes, Librarian and Admin (all users must be one or the other). How do I check to see if an instance of User is of type Admin ? The code below is what I tried before. The issue is that I have code in the AdminUser constructor that I don't want executed unnecessarily. I just need to see if the passed user is of type, Admin .

public boolean isAdmin( User u )
{
    AdminUser a = new AdminUser();
    Class<? extends AdminUser> c = a.getClass();
    return u.getClass() == a.getClass();
}

Answer 1

You can use AdminUser.class .

public boolean isAdmin(final User u)
{
    return u.getClass() == AdminUser.class;
}

Answer 2

Just saying, instanceof works correctly.

public boolean isAdmin( User u )
{
    return (u instanceof Admim);
}

But you can use the class keyword.

public boolean isAdmin( User u )
{
    return u.class == AdminUser.class;
}

But I recommend using instanceof .