Question

please have a look at this code here.

class Vehicle {
    public void printSound() {
        System.out.print("vehicle");
    }
}

class Car extends Vehicle {
    public void printSound() {
        System.out.print("car");
    }
}

class Bike extends Vehicle{ // also tried to extend Car
    public void printSound() {
        System.out.print("bike");
    }
}

public class Test {
    public static void main(String[] args) {
        Vehicle v = new Car();
        Bike b = (Bike)v;
        v.printSound();
        b.printSound();

        Object myObj = new String[]{"one", "two", "three"};
        for (String s : (String[])myObj) System.out.print(s + ".");


    }
}

Executing this code will give ClassCastException saying inheritance.Car cannot be cast to inheritance.Bike.

Now look at the line Object myObj = new String[]{"one", "two", "three"};. This line is same as Vehicle v = new Car(); right? In both lines we are assigning sub class object to super class reference variable. But downcasting String[]myObj is allowed but (Bike)v is not. As mentioned in the comment I also tried to extend Car using bike. According to some discussion here, Bike is not a car because it is extending vehicle. If I extend Car by a Bike, then it means Bike is a type of Car, still the exception remains.

Please help me understand what is going on around here.

P.s – please don’t take the whole convert car to bike, bike to car literally 😉

Answer 1

No, the code provided differs from the code in your example in a basic sentence:

//you're declaring a Object class variable
Object myObj = new String[]{"one", "two", "three"};
//you're declaring a Car class instance, not a Vehicle
Vehicle v = new Car();

They’re not the same. In the first example, you’re using the parent class to save the value, in the second you’re using a child class and assigning a parent value, but the object will be a child, not the parent.

Let’s see the classes composition for further explanation:

Object
- String[]
- Vehicle
  - Car
  - Bike

As you can see, every String[] will be a Object, now every Car will be a Vehicle, but a Car is not a Bike. Explaining it with code

Vehicle v = new Car();
//v contains an instance of Car
Car c = v;
//a Car is not a Bike, this line will throw an error
Bike b = c;
//v2 contains an instance of Vehicle
Vehicle v2 = new Vehicle();
//a Car is a Vehicle
Car c2 = v2;
//a Bike is a Vehicle
Bike b2 = v2;