Question

This question is about java program. Please show the output and the detail code and comment.And the output (the test mthod )must be all the true!

Thank you!

And the question is contain 7 parts:

Question 1
Create a Shape class with the following UML specification:

(All the UML "-" means private and "+" means public)
+------------------------------------+
| Shape |
+------------------------------------+
| - x: double |
| - y: double |
+------------------------------------+
| + Shape(double x, double y) |
| + getX(): double |
| + getY(): double |
| + area(): double |
| + testShape(): void |(this method is static)
+------------------------------------+
where the x and y instance variables store the position of the central point of the shape. The area method computes as result the area of the shape: unfortunately an unknown shape has an unknown area (we only know how to compute the area of specific shapes, like triangles, for example) so the area method just prints a message “An unknown shape has an unknown area!” and returns a meaningless result such as -1.0 (because the area method must return something which is of type double). The testShape method is static.
Add the following code to your program to test the Shape class:
public class Start {
public static void main(String[] args) {
Shape.testShape();
}
}
Question 2
Add a Circle class that derives from the Shape class and has the following UML specification:
+---------------------------------------------+
| Circle |
+---------------------------------------------+
| - radius: double |
+---------------------------------------------+
| + Circle(double x, double y, double radius) |
| + area(): double |
| + testCircle(): void |(static)
+---------------------------------------------+
Use Math.PI to compute the area of a circle.
Do not forget to change the main method of the Start class to run the unit tests of the new Circle class.
Question 3
Add a Dot class that derives from the Shape class and has the following UML specification:
+----------------------------------+
| Dot |
+----------------------------------+
+----------------------------------+
| + Dot(double x, double y) |
| + area(): double |
| + testDot(): void |(static)
+----------------------------------+
Do not forget to change the main method of the Start class to run the unit tests of the new Dot class.
Question 4
Add two new classes Rectangle and Square. Rectangle derives from Shape and Square derives from
Rectangle. Rectangle has the following UML specification:
+--------------------------------------------------------------+
| Rectangle |
+--------------------------------------------------------------+
| - width: double |
| - length: double |
+--------------------------------------------------------------+
| + Rectangle(double x, double y, double width, double length) |
| + area(): double |
| + testRectangle(): void |(static)
+--------------------------------------------------------------+
The constructor for Square takes three arguments: the x and y positions of the center of the square, and the size of
the square.
Does the Square class need its own area method?
Do not forget to change the main method of the Start class to run the unit tests of the new Rectangle and
Square classes.
Question 5
We now want to be able to manipulate many shapes together in our software, not just one shape at a time. So add a
ManyShapes class to your program with the following UML diagram:
+---------------------------+
| ManyShapes |
+---------------------------|
| - allShapes: ArrayList |
+---------------------------+
| + ManyShapes() |
| + addShape(Shape s): void |
| + listAllShapes(): void |
| + testManyShapes (): void |(static)
+---------------------------+
The allShapes instance variable is of type ArrayList which is a class provided to you by Java that you need to
import into your program using: import java.util.ArrayList;
You can then define the allShapes instance variable like this: private ArrayList allShapes;
In the ManyShapes constructor you need to create a new ArrayList object and store it in the instance variable
allShapes, like this: this.allShapes = new ArrayList();
(if you forget to do this then the instance variable allShapes will point at nothing and you will get an error when you
run your program and you try to call a method of the nonexistent arraylist object).
An ArrayList object works both like an array and like a list, in which you can store as many other objects of type
Object as you want:
 you can add a new object o to the arraylist by using the add(o) method of the arraylist;
 you can get the number of elements in the arraylist by using the size() method of the arraylist;
 you can access a specific element of the arraylist at index i by using the get(i) method of the arraylist
(element indexes start at zero in an arraylist).
The addShape method takes a shape as argument and adds it to the arraylist.
The listAllShapes method prints on the screen the area of each shape in the arraylist, one by one, using a loop. For
example, if the arraylist currently contains a Square object of size 5 and a Dot object then the listAllShapes
method should print:
Shape has area 25.0
Shape has area 0.0
Here is the code of the testManyShapes method:
public static void testManyShapes() {
ManyShapes m = new ManyShapes();
m.addShape(new Circle(1.2, 3.4, 4.0)); // Upcast from Circle to Shape.
m.addShape(new Dot(1.2, 3.4)); // Upcast from Dot to Shape.
m.addShape(new Rectangle(1.2, 3.4, 4.0, 5.0)); // Upcast from Rectangle to Shape.
m.addShape(new Shape(1.2, 3.4));
m.addShape(new Square(1.2, 3.4, 5.0)); // Upcast from Square to Shape.
m.listAllShapes();
}
Do not forget to change the main method of the Start class to run the unit tests of the new ManyShapes class.
Question 6
The listAllShapes method tells us the area of every shape in the arraylist but it does not tell us the type of the
shapes in the arraylist. Modify the listAllShapes method to tell us both the area and the type for each shape in the
arraylist. For example, if the arraylist currently contains a Square object of size 5 and a Dot object then the
listAllShapes method should print:
Square has area 25.0
Dot has area 0.0
Use the instanceof operator in the listAllShapes method to determine the type of each shape.
Question 7
Using instanceof in the listAllShapes method works fine, but there is a nicer, more object-oriented way to do
the same thing: just have every shape object tell about itself when it is asked! To do this, add a new method toString
to the Shape class that overrides the toString method which is inherited by the Shape class from the Object
class. This method should then return the string “Shape has area XXX”, where XXX is the result of the area
method from the same class Shape. Then override the toString method in every subclass of Shape to return the
right string for the subclass in a similar way.
After you have added the toString method to the Shape class and all its subclasses, delete all the instanceof
tests in the listAllShapes method of the ManyShapes class and use System.out.println to directly print
every element of the arraylist (System.out.println will then automatically call the toString method of each
object that you are printing; no downcast is needed then because Java’s dynamic dispatch will automatically call the
right toString method coming from the right class for each object stored in the arraylist that you are printing).

Answer 1

/*************************Shape.java**********************/

package shape;

public class Shape {

   private double x;
   private double y;

   public Shape(double x, double y) {
       this.x = x;
       this.y = y;
   }

   public double getX() {
       return x;
   }

   public double getY() {
       return y;
   }

   public double area() {

       System.out.println("An unknown shape has an unknown area!");

       return -1;

   }

   public static void testShape() {

   }

   @Override
   public String toString() {
       return "Shape has area " + area();
   }

}
/**********************************Circle.java************************/

package shape;

public class Circle extends Shape {

   private double radius;

   public Circle(double x, double y, double radius) {
       super(x, y);
       this.radius = radius;
   }

   public double area() {

       return Math.PI * radius * radius;
   }

   public static void testCircle() {

   }
  
   @Override
   public String toString() {
       return "Circle has area " + area();
   }
}
/*************************************Dot.java***************************/

package shape;

public class Dot extends Shape {

   public Dot(double x, double y) {
       super(x, y);
   }

   public double area() {

       return 0;
   }

   public static void testDot() {

   }

   @Override
   public String toString() {
       return "Dot has area " + area();
   }
}
/***********************************Rectangle.java*******************************/

package shape;

public class Rectangle extends Shape {

   private double width;
   private double length;

   public Rectangle(double x, double y, double width, double length) {
       super(x, y);
       this.width = width;
       this.length = length;
   }

   public double area() {

       return length * width;
   }

   public static void testRectangle() {

   }
   @Override
   public String toString() {
       return "Rectangle has area " + area();
   }
}
/************************************Square.java****************************/

package shape;

public class Square extends Shape {

   private double size;

   public Square(double x, double y, double size) {
       super(x, y);
       this.size = size;
   }

   public double area() {

       return size * size;
   }

   public static void testSquare() {
      
   }
   @Override
   public String toString() {
       return "Square has area " + area();
   }
}
/*********************************ManyShapes.java**************************/

package shape;

import java.util.ArrayList;

public class ManyShapes {

   private ArrayList<Shape> shapes;

   public ManyShapes() {

       shapes = new ArrayList<>();
   }

   public void addShape(Shape s) {

       shapes.add(s);
   }

   public void listAllShapes() {

       for (Shape shape : shapes) {

           System.out.println(shape.toString());
       }
   }
  
   public static void testManyShapes() {
      
       ManyShapes m = new ManyShapes();
       m.addShape(new Circle(1.2, 3.4, 4.0)); // Upcast from Circle to Shape.
       m.addShape(new Dot(1.2, 3.4)); // Upcast from Dot to Shape.
       m.addShape(new Rectangle(1.2, 3.4, 4.0, 5.0)); // Upcast from Rectangle to Shape.
       m.addShape(new Shape(1.2, 3.4));
       m.addShape(new Square(1.2, 3.4, 5.0)); // Upcast from Square to Shape.
       m.listAllShapes();
   }
}
/*************************Start.java**********************/

package shape;

public class Start {

   public static void main(String[] args) {
      
       ManyShapes.testManyShapes();
   }
}
/***********************output**********************/

Circle has area 50.26548245743669
Dot has area 0.0
Rectangle has area 20.0
An unknown shape has an unknown area!
Shape has area -1.0
Square has area 25.0

Please let me know if you have any doubt or modify the answer, Thanks:)