为子类设置超类属性

Question

So I'm having a bit of an issue getting my properties to set properly in a super class type scenario.

I have 2 classes such that class B is a specialized version of class A, let's say...

public class A {
    private String name;
    private int id;
    ...
} 

public class B extends A {
    private Date time;
    private int status;
    ...
}

Now what I'm trying to do is use a method that is used to set properties in A from a result set, but instead set them in an instance of B.

public A setProperties(ResultSet rs) {
    A a = new A();
    a.setName(rs.getString(...));
    ...
    return a;
}

I have tried taking the return from this and casting it as a B, but of course not all A's are B's... so that doesn't work. I have also tried adding another parameter to the setProperties method so that it takes in an A and returns an A, that way I can use polymorphism to get my B back, but then all my values were nulled out.

I'm at a loss here, any recommendations are greatly appreciated.

Answer 1

Declare the method in the superclass. The subclass will override this method and then invoke super.foo(ResultSet rs) , where foo(...) is the overridden method. Therein, you can parse the ResultSet and set the object's fields.

Example -

class Foo{
    void setProperties(final ResultSet rs){
        // do stuff
    }
}

final class Bar extends Foo{
    @Override
    final void setProperties(final ResultSet rs){
        // do stuff
        super.setProperties(rs);
    }
}

For more information, see Using the Keyword super .