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How downcasting is possible in java?

 It helps to first define exactly what a downcast is. Its actually pretty simple suppose you have a base class, and a class that derives from that base class either directly or indirectly. Then, anytime an object of that base class type is type cast into a derived class type, it is called a downcast. The reason its called a downcast is because of the way that inheritance diagrams are normally written base classes are at the top and derived classes are down below the base classes. So, in downcasting, you are going down the inheritance diagram by taking an object of a base class (at the top), and then trying to convert into the type of one of the derived classes (going down). The key word there is trying because downcasting does not always make sense depending on the code being written. 

example:

 we have the following Java code in which a downcasting is being performed:

class home{ /* ... */}

class room extends home { /* ... */ }

public class Test {

public static void main (String args[ ]) {

home p = new home ( );

/*this is a downcast since the Parent class

object, "p" is being cast to a room type,

and room derives from the home class */

room c = (room) p;

}

}

Which of the following will happen with the code above:

1. It will compile and run without any errors
2. It will throw a compile time exception
3. It will throw a Runtime exception
 

In the code above, this line is where the downcast is being performed:

room c = (room) p;


  

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