ニュートン反復ルートアルゴリズム

public class Test extends Thread {

	
	private static float a = 121;
	
	public static void main(String[] args){
		float x0 = 1;
		float x1 = (float) (x0+(a/x0-x0)*0.5);
		float diff = x1 - x0;
		while(true){
			x0 = (float) (x1+(a/x1-x1)*0.5);
			diff = x1 -x0;
			if(diff<0.0001 && diff>-0.0001){
				break;
			}
			x1 = (float) (x0+(a/x0-x0)*0.5);
			diff = x1 -x0;
			if(diff<0.1 && diff>-0.1){
				break;
			}
		}		
		System.out.println(x0);
	}
}