public abstract class Shape I

public abstract double perimeter$()$;

public abstract double area$()$;

$$

$($d$)$ Solution

public class Circle extends Shape $||$

private double radius;

public double perimeter$()$ I

return $2*$ Math.PI $*$ radius;

$\}$

public double area $0($

return Math.PI $*$ radius $*$ radius;

$1$

$1$

$($e$)$ Solution

public class Rectangle extends Shape $\{$

private double length, width;

public double perimeter$()($

return $2*($length $+$ width$)$;

I

public double area$()($

return length $*$ widtht;

What is abstract class shape means $?$