I've been working on this for one hour, just can't get it.

I have a Vector2d class:

public class Vector2d
{
    public double x = 0.0;
    public double y = 0.0;

    ....
}

This vector class has a rotate() method which is causing me trouble.

The first snippet seems to make the x and y values smaller and smaller. The second one works just fine! Am I missing something simple here?

public void rotate(double n)
{
    this.x = (this.x * Math.cos(n)) - (this.y * Math.sin(n));
    this.y = (this.x * Math.sin(n)) + (this.y * Math.cos(n));
}

This works:

public void rotate(double n)
{
    rx = (this.x * Math.cos(n)) - (this.y * Math.sin(n));
    ry = (this.x * Math.sin(n)) + (this.y * Math.cos(n));
    x = rx;
    y = ry;
}

I just can't spot any difference there