Question

Create an application that provides a solution for problem 20.8 In addition to requirements specified in the description. The class must satisfy the following Default Constructor Two argument constructor for data used to initialize "first" and "second" "toString" method for displaying the "first" and "second" data elements Creates a "Comparator" object (to be used by the sort method; i.e. create an instance of a class that implements the interface [must override "compare" and "equals" methods]) The application must create an ArrayList of 5 Pair objects and then display the contents in sorted order largest to smallest, based on the method used to compare "Pair" objects. The class only supports types that extend Number. Assume the "Pair" objects contain x, y coordinates. Therefore calculate the distance from a 0,0 coordinate to determine the sorting order (i.e., ascending, smallest distance to largest distance).

Please include the problem from 20.8 in the coding, I can't figure out how to incorporate the array list into the former problem.

20.8 (Generic Class Pair) Write a generic class Pair which has two type parameters--F and S--each representing the type of the first and second element of the pair, respectively. Add get and set methods for the first and second elements of the pair. [Hint: The class header should be public class Pair<F, S>.]

Answer 1

Hi. I have answered this question before. 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

// Pair.java

import java.util.ArrayList;

import java.util.Collections;

import java.util.Comparator;

import java.util.Random;

public class Pair<F extends Number, S extends Number> {

      private F first;

      private S second;

      public Pair() {

            first = null;

            second = null;

      }

      public Pair(F first, S second) {

            this.first = first;

            this.second = second;

      }

      public F getFirst() {

            return first;

      }

      public void setFirst(F first) {

            this.first = first;

      }

      public S getSecond() {

            return second;

      }

      public void setSecond(S second) {

            this.second = second;

      }

      @Override

      public String toString() {

            return "(" + first + ", " + second + ")";

      }

      @Override

      public boolean equals(Object other) {

            if (other instanceof Pair) {

                  Pair p = (Pair) other;

                  if (first.equals(p.first) && second.equals(p.second)) {

                        //equal object

                        return true;

                  }

            }

            //not equal

            return false;

      }

      public static void main(String[] args) {

            // creating a Comparator object to sort Pair of two Integers

            Comparator<Pair<Integer, Integer>> comp = new Comparator<Pair<Integer, Integer>>() {

                  @Override

                  public int compare(Pair<Integer, Integer> p1,

                              Pair<Integer, Integer> p2) {

                        // finding distance between origin and points specified by pairs

                        // using formula sqrt(x^2 + y^2)

                        double dist1 = Math.sqrt(p1.getFirst() * p1.getFirst()

                                    + p1.getSecond() * p1.getSecond());

                        double dist2 = Math.sqrt(p2.getFirst() * p2.getFirst()

                                    + p2.getSecond() * p2.getSecond());

                        // checking if first pair has less distance from origin than

                        // second

                        if (dist1 < dist2) {

                              return -1; // p1 should come first

                        }

                        if (dist1 > dist2) {

                              return 1; // p2 should come first

                        }

                        return 0; // equal pair

                  }

            };

            // creating an array list of Pair objects

            ArrayList<Pair<Integer, Integer>> pairList = new ArrayList<Pair<Integer, Integer>>();

            // using a Random object, creating 5 random coordinates Pair objects,

            // adding to array list

            Random random = new Random();

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

                  Pair<Integer, Integer> p = new Pair<Integer, Integer>(

                              random.nextInt(10), random.nextInt(10));

                  pairList.add(p);

            }

            // displaying before sorting

            System.out.println("List before sorting: ");

            System.out.println(pairList);

            // sorting and displaying after sorting

            Collections.sort(pairList, comp);

            System.out.println("List after sorting: ");

            System.out.println(pairList);

      }

}

/*OUTPUT*/

List before sorting:

[(8, 6), (6, 8), (3, 1), (2, 4), (7, 0)]

List after sorting:

[(3, 1), (2, 4), (7, 0), (8, 6), (6, 8)]