Polymorphism

AP Computer Science A· difficulty 3/5

public abstract class Shape {
    public abstract double area();
    public String describe() { return "Area=" + area(); }
}
public class Square extends Shape {
    private double side;
    public Square(double s) { side = s; }
    public double area() { return side * side; }
}
// Usage:
Shape s = new Square(3);
System.out.print(s.describe());

What is printed?

A
$Area=0.0$
B
$Area=9.0$
check_circle
C
$Compile error$
D
$Area=3.0$

Explanation

describe() is inherited from Shape and calls area(). Polymorphic dispatch invokes Square's area, returning 9.0.

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