Thread: Trick question?

I highly suggest you write a small program that does exactly that, and see what happens. Then you can show us!

I'm not even sure I'm breaking this down to myself correctly...
Given a class A and another (B) that inherits from it, if you have a method that casts B to A and invokes a method x() that both A and B implement, which class's implementation is invoked?

Basically wouldn't this just be a function call that is within class B, but it really just calls a function in class A, therefore there is no confusion on the matter, it could generically be written as "ClassA.FunctionX()"?

I don't think I'm even understanding this correctly...

This is an extremely common example of inheritance, and it's used all the time- not just as an interview question.

For example, say you have a class Animal that has some default behaviors (let's say eat, speak, and walk)-

public class Animal{
   public void speak(){
      System.out.println("The animal made a noise!");
   }
    public void eat(){
      System.out.println("The animal ate its food.");
   }
   public void walk(){
      System.out.println("The animal took a step.");
   }
}

So far so good, right? But then you want a specific sub-type of Animal, let's say Cat, to override the behaviors for eat and speak:

public class Cat extends Animal{
   public void speak(){
      System.out.println("The cat meowed!");
   }
    public void eat(){
      System.out.println("The cat ate a mouse.");
   }
}

Okay, so now what would you want to happen with this:

Animal cat = new Cat();
cat.speak();
cat.walk();
cat.eat();

See, the instance of Cat IS AN Animal, but it also has its own behavior.

This is one of the most commonly used features of OOP- extending a class to change a part of its behavior. For example, the most common way to do painting is by extending JPanel and overriding the paintComponent() method- everything else stays the same, and the program treats the Object as a normal JPanel, until the painting is done- then the code in the child class is called.

This is actually a pretty decent interview question, as the only real way to understand what I'm talking about is through the experience of actually using it. And I suggest you do get some more practice before your next interview, as this is just the tip of the iceburg- we haven't touched the ability to call parent class methods from a child, or what happens when a method is static, or mixing child and parent methods, or abstract methods, or...