Question

need some help on these a little contested
right now the answers i have are

18 : d

19 : e

20 : c

would appriacte why i am right or wrong thank you

19. The default constructor sets x and y to (0,0) by calling the second constructor. What could be used to replace / missing code */ so that this works as intended? a b = = 0; 0; this(0, 0); this (x, y); a = b = x; y; x y = a; = b;

sorry i added the picture of 17 by mistake

Answer 1

Question 18:

Answer: (d)

Explanation: Even though you haven't provided the image for option (d), it should be like return (x == p.x && y == p.y);

Question 19:

Answer: (e)

Explanation: Only option (e) initializes the values of x and y to the values provided in arguments a and b.

Question 20:

Answer: (c)

Explanation: a mutator sets the values of instance variables (variable of the object) to the one provided as arguments, and this is only done by option (c).

Code:

// Point.java

public class Point {
   private double x;
   private double y;

   // this default constructor will call the second constructor
   public Point() {
       this (0, 0);
   }
   // this second constructor sets the values of x and y
   // to the one provided as arguments
   public Point(double a, double b) {
       x = a;
       y = b;
   }
   // this mutator changes the values of x and y by the one provided
   public void setCoordinates(double a, double b) {
       x = a;
       y = b;
   }
   // equals method checks equality of coordinates of point object provided
   // as arguments by the coordinates of the current object and returs true if
   // both are equal else returns false
   public boolean equals(Point p) {
       return (x == p.x && y == p.y);
   }

   // this is an extra method added by me, to print the coordiantes
   public String toString() {
       return ("x: "+x+" y: "+y);
   }  
}

// PointTest.java

public class PointTest {
   public static void main(String[] args) {
       // declaring three objects of Point Class
       Point p1 = new Point(1, 2);
       Point p2 = new Point();
       Point p3 = new Point(1, 2);

       // priting the three objects
       System.out.println(p1);
       System.out.println(p2);
       System.out.println(p3);

       // printing the equality of three objects
       System.out.println();
       // this should print false
       System.out.println("p1 equals p2: "+p1.equals(p2));
       // this should also print false
       System.out.println("p2 equals p3: "+p2.equals(p3));
       // this should print true
       System.out.println("p3 equals p1: "+p3.equals(p1));
   }
}

OUTPUT: