Not happy with the explanation given..

[Rajesh k Jha]

Interface Inter
{
}
class Base implements Inter
{
}
class Derived extends Base
{
}
public class Test
{
public static void main(Strng[] args)
{
Base b=new Base();
Derived d=new Derived();
Inter i=(Base)b;
i=(Base)d;
Derived bd=(Derived)b;//1
b=(Base)i;//2
}
}

It says commented line 2 is correct and says "commented line 2 will compile because the interface type variable has been case as Base type" Can somebody elaborate the concept...how is this correct

[Andrew Monkhouse]

When you copy a question from a book, mock exam or other source, then you are required to quote your sources - so, please tell us where you copied this question from.

[Seetharaman Venkatasamy]

    

class A
{
	
}

public class Test extends A{	
	
	  public static void main(String args[]) {	
		Test b = (Test)new A();//ClassCastException Here
		 A a = (A)new Test();//fine
	  }	  
}

Try above code . Shortly, You can put subtype object into super type but not vice versa

Hope this helps

[Jason Irwin]

Please use code tags.
Also, your code will not compile due to typographical errors.

Have you tried running this code to see what happens for yourself?

Base implements Inter, it passes the IS-A test.
Thus casting from any reference to Inter to Base could work, so the compiler allows it. The compiler is no aware of the instance "i" refers to, only the reference type.

In this example "i" refers to a Derived instance and Derived extends Base, so it passes the IS-A test for Base and for Inter (through inheritance).3
Thus the cast to Base will is acceptable at compile time and will work at run time.

If you added another class (e.g. "Other") and made the implement Inter, then set "i" to an instance of Other; you would get a class cast at line 2 at run time.
Although "Other" IS-A Inter (and thus passes compilation), it is not IS-A Base; so you get the exception.

[Rajesh k Jha]

I got this question from Whizlab mock test 1.5

[Rajesh k Jha]

Thanks, It gave me the concept of IS-A relationship, and i got the satisfaction