Inner Classes

Q1:
class Boo 
{
    Boo(String s) { }
    Boo() { }
}
class Bar extends Boo 
{
    Bar() { }
    Bar(String s) {super(s);}
    void zoo() 
    {
    // insert code here
    }
}
which one create an anonymous inner class from within class Bar?

A Bar f = new Boo(String s) { };

B Boo f = new Boo.Bar(String s) { };

C Boo f = new Bar() { };

D Boo f = new Boo(24) { };

ANS:A - Boo f = new Boo(24) { };

Option B is correct because anonymous inner classes are no different from any other class when it comes to polymorphism. That means you are always allowed to declare a reference variable of the superclass type and have that reference variable refer to an instance of a subclass type, which in this case is an anonymous subclass of Bar. Since Bar is a subclass of Boo, it all works. Option A is incorrect because it passes an int to the Boo constructor, and there is no matching constructor in the Boo class. Option C is incorrect because it violates the rules of polymorphism—you cannot refer to a superclass type using a reference variable declared as the subclass type. The superclass is not guaranteed to have everything the subclass has. Option D uses incorrect syntax.



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