Can't use value in different classes

Question

I know how to put value from one class to another. Just here it doesn't work. I can't understand why.

Please help me to find a bug.

When I try to get value:

 c = new CartesianCoordinate(x, y);
 x = c.getX();

It is always zero.

public class Velocity
{
    // instance variables - replace the example below with your own
    private double x;
    private double y;
    /**
     * Constructor for objects of class Velocity
     */
    public Velocity(CartesianCoordinate c)
    {
        // initialise instance variables
        c = new CartesianCoordinate(x,y);
        x = c.getX();
        System.out.println(c.getX());
        System.out.println(c.getY());
        System.out.println(c.x);

     }

    public double getX()
    {
        return x;
    }

Here is my CartesianCoordinate:

    public class CartesianCoordinate
    {
       // instance variables - replace the example below with your own
       public double x;
       public double y;

       /**
        * Constructor for objects of class CartesianCoordinate
        */
       public CartesianCoordinate(double x, double y)
       {
           // initialise instance variables
           this.x = x;
           this.y = y;
       }




    public void setX(double x)
    {
        // put your code here
        this.x = x;
    }

    public void setY(double y)
    {
        this.y = y;
    }

    public double getX()
    {
        return x;
    }

    public double getY()
    {
        return y;
    }
}

Answer 1

In following line:

c = new CartesianCoordinate(x,y);

you are creating a new instance with the values of Velocity instance private fields x and y, which are set to 0 by default.

By the way, it makes no sense to pass a CartesianCoordinate instance as the constructor parameter, then re-initialising it inside the constructor itself. Either you pass x and y values like public Velocity(int x, int y), or you just assign the coordinate.

In the future, you'll want to know about Point2D class.