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].
Boo f = new Boo(24) { };
[B].
Boo f = new Bar() { };
[C].
Bar f = new Boo(String s) { };
[D].
Boo f = new Boo.Bar(String s) { };
Answer: Option B
Explanation:
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.
C is incorrect indeed, but not due to polymorphism, but due to invoking it with wrong arguments (String cannot be resolved to a variable). Making it Bar f = new Boo (new String () ) { }; makes it incorrect due to polymorphism.
Pooja said:
(Jun 21, 2016)
Haven't got this yet!
Sami said:
(Mar 7, 2017)
You are absolutely right @Javac.
The argument in Boo should be string reference or value but not a declaration!
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