Polymorphism

AP Computer Science A· difficulty 3/5

import java.util.*;
public class A { public String f() { return "A"; } }
public class B extends A { public String f() { return "B"; } }
List<A> list = new ArrayList<>();
list.add(new B());
A x = list.get(0);
System.out.println(x.f());

What is printed?

A
$B$
check_circle
B
$AB$
C
$Compile-time error$
D
$A$

Explanation

Stored as B, accessed via A reference; dynamic dispatch picks B.f.

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