public abstract class Shape { public Shape() { } public abstract double area() ; public String who() { return "Shape" ;

[answerhappygod]

public abstract class Shape {
public Shape() { }
public abstract double area()
;
public String
who() { return "Shape" ; }
}
public class Circle extends Shape {
private int radius ;
public Circle( int r )
{
radius = r ;
}
@Override
public double area()
{
return Math.PI * radius * radius
;
}
}
public class Square extends Shape {
private int _sideLength ;
public Square( int sideLength
)
{
/* TODO question 45 */
}
@Override
public double area()
{
return _sideLength *
_sideLength ;
}
}
Implement the Square constructor, and make sure it
throws an exception when the input parameter is not a valid length.
The input parameter must be positive to be considered
valid.