Question

Consider the following class Point which represents a point in Cartesian coordinate system. The class has two instance variables x and y which represent its position along the x-axis and y-axis. The constructor of the class initializes the x and y of the point with the specific value init; the method move() moves the point as specified by its parameter amount.

Using the implementation of the class Point information and write its specification. The specification of the class includes the specification of its methods. Each method specification contains the method's name, signature, informal English description, precondition, postcondition (return), throws list.

class Point{

   private int x;

   private int y;

   public Point(int init){

                        x = init;

                        y = init;

   }

   public void move(int amount){

                        if(amount < 0 )

                                    throws new IllegalArgumentException();

                        else if(amount = 0)

                                    return;

                        else{

                                    x += amount;

                                    y += amount;

                        }

   }

}

Answer 1

/**
 * Below class represent a cartesian system point, where each point
 * has a x coordinate along with a y-coordinate.
 *
 */
public class Point {

    /**
     * Instance variable that holds the value of x-coordinate of the point
     */
    private int x;

    /**
     * Instance variable that holds the value of y-coordinate of the point
     */
    private int y;

    /**
     * This method constructs a Point object using an initial position.
     * both x and y coordinates are assigned with initial position
     * This method is known as Constructor
     * @param init: the intial position
     */
    public Point(int init) {
        x = init;
        y = init;
    }

    /**
     * By passing a specific amount, we can move the point in both
     * x and y axis. The point is shifter by adding this amount on
     * both x and y coordinates
     * @param amount
     * @throws IllegalArgumentException : If the given amount is negative, 
     * then it results in an error.
     */
    public void move(int amount) {

        // check if error condition
        if (amount < 0)
            throw new IllegalArgumentException();

        // if there is nothign to move
        else if (amount == 0)
            return;

        // move the points as asked by amount
        else {
            x += amount;
            y += amount;
        }
    }
}