Java : อยากรู้วิธีล็อคจำนวนเลขทศนิยมเวลาคำนวณ หรือหาคำตอบออกมา

import java.util.*;
public class JavaApplication1 {
    public static double a;
    public static double b;
    public static double x;
    public static double news = 0;
    public static double old = 0;
    public static double error;
    public static void main(String[] args) {
        Scanner data = new Scanner(System.in);
        System.out.print("Input a : ");
        a = data.nextDouble();
        System.out.print("Input b : ");
        b = data.nextDouble();
        double temp;
        double fa = Math.acos(a)-0.75;
        double fb = Math.acos(b)-0.75;
        if (fa*fb>0)
            System.out.println("Wrong value of a,b");
        if (fa<fb)
                    {temp = b;
                     b = a;
                     a = temp;}
        double answer = cal();
        //System.out.println("Answer of y=cosX-0.75 is "+answer);
        System.out.printf("Answer = %.4f\n", answer);
    }//main
    public static double cal() {
        for (int i=1;i>0;i++)
        {x = (a+b)/2;
         old = news;
         news = x;
         error = news - old;
         double y = Math.acos(x)-0.75;
         if (y>0)
             a=x;
         else 
             b=x;
         if (Math.abs(error)<0.0001)
             break;
        }//for
        double ans = news;
        return ans;
    }//cal
    
}