Complete the surfaceArea() method of the Circle class. public class Circle {

private double radius;

// constructor

// postcondition: the instance variable is initialized

public Circle(double rad)

{

radius = rad;

}

// postcondition: returns the surface area of a sphere with radius equal to this circle's

// radius, according to the formula 4 PI r^2, where PI is the value of pi (3.1415...),

// r is the radius of the circle, and "^2" means raised to the second power.

// Operands are multiplied.

// Use the constant Math.PI in your calculation to represent PI

public double surfaceArea()

{

}

}