public class practice {    //圆周率计算器    public static void main(String[] args) {        double sum = (double) 2/3;        System.out.println("请指定你想计算的项数:");        Scanner sc = new Scanner(System.in);        int m = sc.nextInt();        for (int i = 3; i < m; i++){            //取小数进行计算            double cal = (double) 1/((2 * i)-1);            if (i % 2 == 0){                sum -= cal;            }else{                sum += cal;            }        }        System.out.println("计算到第"+m+"项的圆周率Pi为:"+(4*sum));    }}