Question

I am taking a computer science course and my professor teaches much too fast. I am feeling so overwhelmed and lost. Very worried as well, as I am trying my very hardest in this class but just cant seem to grasp it. I have just been given this assignment.... Can someone explain what I am supposed to do? Is there one class? two? are there supposed to be multiple files? :( thanks!

• Write a Java class called a Circle that represents a circle. This circle has a field radius of type double.

• (a) Import this class to a driver class circleDriver, and create an object of circle type. (b) What is its radius going to be? (c) Why?

• Write a constructor that instantiates a circle with radius 3.5

• Write a constructor that instantiates a circle with given radius

• Test these constructors in circleDriver by initializing the constructors (3) as C1 and (4) as C2, and then printing C1.radius and C2.radius.

• (a) What error does your program throw if you try to give your constructor a return type? (b) What does it mean? (one line)

• (a) Write assessor (getter) for the field radius for this circles and test it in circleDriver: but before doing so, answer the following questions: (b) What should its return type be? (c) Why? (d) Why are you not passing any parameters to it?

• (a)Change the fields of this circle in such a way that they are encapsulated, using private access modifier. (b)Why is it a good idea to encapsulate the fields? (one line) (c) what errors would printing C1.radius throw? (d) why?

• (a)Write a class method called ‘Print’ to print the radius of Circle using your getter. (b)Test by printing C1’s radius.

• (a) Write a setter to modify the radius value. But before you do that, answer the following questions: (b) what should its return type be? (c) Why? (d) why aren’t we passing any parameters to it?

• Change the radius value of C1 to be 15 and print it with method Print.

• (a) Write a class method that calculates the area of this circle. But before you do that, answer the following questions: (b) what should its return type be? (c) Why? (d) why aren’t we passing any parameters to it?

Answer 1

(a)Change the fields of this circle in such a way that they are encapsulated, using private access modifier.

private double radius;

(b)Why is it a good idea to encapsulate the fields? (one line)

ANS : BECAUSE IT PROTECTS CHANGING VARIABLE VALUE FROM OTHER CLASS and this method is called as encapsulation

(a) What error does your program throw if you try to give your constructor a return type? (b) What does it mean? (one line)

ANS : Constructor are special function without return type and should have same name as class name .If you add return type in constructer you will get error

Void methods cannot return a value

CircleDriver.java

//This is driver class,driver class is main class where main function is placed and called initially
public class CircleDriver {
   public static void main(String[] args) {
      //Test these constructors in circleDriver by initializing the constructors (3) as C1 and (4) as C2, and then printing C1.radius and C2.radius.
           Circle C1=new Circle();//create circle object
           //What is its radius going to be?
           //it will be 0.0,because default value of double variable is 0.0
           System.out.println(C1.radius);//print radius
           //Write a constructor that instantiates a circle with radius 3.5
          Circle C2=new Circle(3.5);//create circle object
           System.out.println(C2.radius);//print radius
           //(b)Test by printing C1’s radius.
           //this will print radius as 0.0 as there is memory associated to C1 object with radius as 0.0
           C1.print();
          //Change the radius value of C1 to be 15 and print it with method Print.
          C1.setRadius(15);
           C1.print();//will print 15.0
           System.out.println(C1.area());//will print 706.5
   }
}

Circle.java

public class Circle {
   double radius;
//parameterized constructer to initialize radius of users choice
  
   public Circle(double radius) {

       this.radius = radius;
   }
//default constructor
   public Circle() {
   }
   //(a) Write assessor (getter) for the field radius for this circles and test it in circleDriver:
   //but before doing so, answer the following questions:
   //(b) What should its return type
   //ITS RETURN TYPE WILL BE DOUBLE AS WE ARE ACCESSING DOUBLE VARIABLE
  
   //(d) Why are you not passing any parameters to it?
   //BECAUSE WE ARE ACCESSING IT'S VALUE OT INITIALIZING IT
   public double getRadius() {
       return radius;
   }

//(a) Write a setter to modify the radius value.
   //But before you do that, answer the following questions:
   //(b) what should its return type be?
  
   //IT's return type will be void as we are using it to just initializing value and not accessing it
  
   //(d) why aren’t we passing any parameters to it?
  
   //WE ARE PASSING PARAMETER TO IT OF DOUBLE TYPE

   public void setRadius(double radius) {
      
       this.radius = radius;
   }
   //(a)Write a class method called ‘Print’ to print the radius of Circle using your getter.
   public void print() {
       System.out.println(getRadius());
   }
   //a) Write a class method that calculates the area of this circle
   //(b) what should its return type be?
   //It should return double ,because we expect result in double from double value
   //(d) why aren’t we passing any parameters to it?
   //Because we want to only access data not to initialize any data
   public double area() {
       //circle area=3.14 * radius * radius;
       double Area=3.14*getRadius()*getRadius();
       return Area;
   }
}

Try executing this program and you will get your query solved :)