Question

PointList Class

Write a class named PointList that keeps a list of Point objects in an ArrayList. The PointList class should accept any object that is an instance of the Point class,, or a subclass of Point. Demonstrate the class in an application.

This is My point class….

public class Point<T>

{

   private T xCoordinate;

private T yCoordinate;

   public Point(T x, T y)

   {

   xCoordinate = x;

   yCoordinate = y;

   }

public void setX(T ){

       xCoordinate = x;

   }

   public void setY(T y) {

       yCoordinate = y;

   }

public T getX(){

       return xCoordinate;

   }

public T getY(){

   return yCoordinate;

   }

}

And this is the starting of my code…my teacher wants it this way

import java.util.ArrayList;

public final class PointList<T extends Point<? extends Number>>

{

ArrayList<T> arrList = new ArrayList<>();

}

Answer 1

Here is the completed code for this problem. Comments are included, go through it, learn how things work and let me know if you have any doubts or if you need anything to change. If you are satisfied with the solution, please rate the answer. Thanks

Note: Since you did not provide any details about the functionalities of PointList class, I have just created methods to add point, remove point, check if a point exists, and a toString method which returns a string containing all points. Also updated Point class to add equals() and toString() methods to make sure it works fine with the new PointList class.

// PointList.java

import java.util.ArrayList;

public final class PointList<T extends Point<? extends Number>> {

      // list of points

      private ArrayList<T> arrList;

      // constructor to initialize empty list

      public PointList() {

            arrList = new ArrayList<T>();

      }

      // method to add a Point to the list

      public void addPoint(T p) {

            arrList.add(p);

      }

      // method to check if a point exists on the list

      public boolean containsPoint(T p) {

            return arrList.contains(p);

      }

      // method to remove a point from the list if exists

      public void removePoint(T p) {

            if (arrList.contains(p)) {

                  arrList.remove(p);

            }

      }

      // method to return the size of the list

      public int size() {

            return arrList.size();

      }

      // returns a string containing all points data

      public String toString() {

            String data = "";

            for (T p : arrList) {

                  data += p.toString() + "\n";

            }

            return data.trim();

      }

}

//updated Point.java file (added equals and toString methods)

public class Point<T>

{

      private T xCoordinate;

      private T yCoordinate;

      public Point(T x, T y)

      {

            xCoordinate = x;

            yCoordinate = y;

      }

      public void setX(T x) {

            xCoordinate = x;

      }

      public void setY(T y) {

            yCoordinate = y;

      }

      public T getX() {

            return xCoordinate;

      }

      public T getY() {

            return yCoordinate;

      }

      // returns true if the parameter is a Point with same values.

      // needed for contains() and remove() methods of array list to work

      public boolean equals(Object ob) {

            if (ob instanceof Point) {

                  Point p = (Point) ob;

                  return this.xCoordinate.equals(p.xCoordinate)

                              && this.yCoordinate.equals(p.yCoordinate);

            }

            return false;

      }

      //returns a String containing point in (x, y) format

      public String toString() {

            return "(" + xCoordinate + ", " + yCoordinate + ")";

      }

}

// Test.java

public class Test {

      public static void main(String[] args) {

            //creating a PointList object

            PointList<Point<Integer>> pList = new PointList<Point<Integer>>();

            //adding some points

            for (int i = 0; i <= 5; i++) {

                  Point<Integer> p = new Point<Integer>(i, 5 - i);

                  pList.addPoint(p);

            }

            //testing all methods in PointList

            System.out.println("Size: " + pList.size());

            System.out.println("Points:");

            System.out.println(pList);

            System.out.println("Contains (2, 3): "

                        + pList.containsPoint(new Point<Integer>(2, 3)));

            System.out.println("Removing (2, 3)");

            pList.removePoint(new Point<Integer>(2, 3));

            System.out.println("Points:");

            System.out.println(pList);

      }

}

//OUTPUT

Size: 6

Points:

(0, 5)

(1, 4)

(2, 3)

(3, 2)

(4, 1)

(5, 0)

Contains (2, 3): true

Removing (2, 3)

Points:

(0, 5)

(1, 4)

(3, 2)

(4, 1)

(5, 0)