Trick question?

Hi there, I'm preparing for an interview with a company, and I came across this question earlier and was wondering peoples' thoughts on it.
I have a fairly solid programming background, but not so much with Java, and as multiple inheritance is not allowed in Java, how would you respond to this question?

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?

At first look, I'm not entirely sure how to answer this. Since I am usually programming in C#, I do believe this would throw an exception, but since this is Java, after some brushing up, wouldn't it be appropriate to say, "since neither A or B are implementing an interface, it would throw an exception?"

Any help/thoughts would be greatly appreciated!!

Thank you!

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...

public static void main(String[] args) {
// TODO code application logic here
A a = new B();
a.callme();
}
}

class A
{
public void callme()
{
System.out.println("A.callme");
}
}
class B extends A
{
public void callme()
{
System.out.println("B.callme");
}
}


results in "b.callme" being printed?
anyone know of a real world example for this other than to tick off someone interviewing? LOL

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)-

Code java:

---

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:

Code java:

---

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:

Code java:

---

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...