Question

I am looking for an algorithm to draw regular polygon like triangle, quadrangle, pentagon, hexagon etc.

I guess it`s basically dealing with the fact that all polygon points are located on the line of the circle.

What`s the algorithm to calculate those N points for Polygon object?
After drawing a regular polygon I need to draw another regular polygon based on the first one but rotated by K degrees.

Answer 1

Use sin and cos:

double theta = 2 * Math.PI / sides;
for (int i = 0; i < sides; ++i) {
    double x = Math.cos(theta * i);
    double y = Math.sin(theta * i);
    // etc...
}

To rotate just add a constant offset to the angle, i.e. theta * i + offset.