CODEWITHSUNDEEP
java
Himanshu Aggarwal
Himanshu Aggarwal

Reputation: 1809

How the instantiation is happening in this java code snippet

my code is

class Alpha
{
public void foo()
    {
    System.out.print("Alpha ");
    }
}

class Beta extends Alpha
{
public void foo()
    {
    System.out.print("Beta ");
    }

public static void main(String[]args)
   {
    Alpha a = new Beta();
    Beta b = (Beta)a;

    a.foo();
    b.foo();
   }
}

Output:-

Beta Beta

i am new to java and this kind of instantiation i have come across for the first time and thats why i am not able to understand why the output is not 

Alpha Beta

if 'a' is the object of class Alpha then why not Alpha's method is being called?

Please help me out.

Upvotes: 1

Views: 93

Answers (5)

groggygreggy
groggygreggy

Reputation: 153

In java, methods are virtual by default. When deciding what method to actually invoke, the type of the underlying object matters, not the type of the reference to the object.

Upvotes: 0

Masood_mj
Masood_mj

Reputation: 1184

You have just one object of type Beta. Casting an object does not make java to use the parent method.

Upvotes: 0

Prasanth
Prasanth

Reputation: 5258

When parent class variable refers child class object, the reference will call child methods.

Upvotes: 0

Jon Lin
Jon Lin

Reputation: 143886

Casting or referencing an Object as its superclass doesn't un-override methods. The foo() method is still being called on a Beta Object, even if you are originally referencing it as an Alpha Object.

Upvotes: 1

Carl
Carl

Reputation: 915

The object that is created is a type Beta, because that's how it was created by new. So, when foo() is called, it's working on a Beta object no matter what you "call" it in your code.

Upvotes: 1

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