Gouraud shade a model from an array of vertices?

Newbie & Debugging Questions
#1

Gouraud shading: http://en.wikipedia.org/wiki/Gouraud_shading
Video: http://www.youtube.com/watch?v=PMgjVJogIbc

I have a model, expressed here:

My engine uses a standard model class, which is setup like this:

	private float[] vertX;
	private float[] vertY;
	private float[] vertZ;
	private float[] norX;
	private float[] norY;
	private float[] norZ;
	private float[] texX;
	private float[] texY;

I only know the math behind flat shading, so this is what I came up with:

public void flatShade() {
	for (int i = 0; i < amountVertices; i+=3) {
		float[] norm = CollisionHelper.getTriangleNormal(vertX[i], vertY[i], vertZ[i], vertX[i + 1], vertY[i + 1], vertZ[i + 1], vertX[i + 2], vertY[i + 2], vertZ[i + 2]);
		norX[i] = norm[0];
		norX[i + 1] = norm[0];
		norX[i + 2] = norm[0];
		
		norY[i] = norm[1];
		norY[i + 1] = norm[1];
		norY[i + 2] = norm[1];
		
		norZ[i] = norm[2];
		norZ[i + 1] = norm[2];
		norZ[i + 2] = norm[2];
	}
}

And while this works for light calculations (as seen in the picture above), it looks odd, as the triangles which share vertices have normals facing different directions.

What should I do for proper gouraud shading?