在超类对象的向量中访问子类方法

Question

I am using a vector to store objects of an abstract superclass. I need to access a method(s) within the derived subclasses of each object in the vector. I will be using instanceof in order to differentiate which subclass each object is a part of.

I do not have permission to write to the abstract class.

Currently the compile error I am getting is:

Error: cannot find symbol symbol: method <mySubclassMethod>() location: class <MyAbstractClass>

What is the most effective way of going about accessing the subclass methods of each object within my vector?

Answer 1

You need to cast the object to the subclass inside of an instanceof guard.

if (obj instanceof MySubclass)
    ((MySubclass)obj).mySubclassMethod();

More broadly, if the method should be available in all of your subclasses, you should add it to the abstract superclass. Then, when you call the method on the 'uncasted' abstract superclass object, it will use the implementation from the proper subclass.

public abstract class MySuperclass {
    public abstract void mySubclassMethod();
    ...
}

public class MySubclass extends MySuperclass {
    @Override
    public void mySublcassMethod() { ... }
    ...
}
...

MySuperclass obj = [actually a Subclass];
obj.mySubclassMethod(); // uses the implementation from MySubclass

Answer 2

I think what you want to do is to create the method as abstract in your superclass. Then, what you will do is override this method in each of your subclasses. This will allow you to access that method for all the different objects in that vector of yours.

I'm assuming this method will vary depending on your subclass, otherwise, why wouldn't you just write that method in the superclass in the first place.