Java-Pi的几种实现

public class Main {
    public static void main(String[] args) {
        gailv();
    }

    //无穷级数计算 1 - 1/3 + 1/5 -1/7+..... 
    public static void wuqiongjishu() {
        double p1 = 1, p2 = 0;
        double i = 1;
        double flag = 1;
        double diff = Math.pow(0.1, 9);
        while (Math.abs(p1 - p2) >= diff) {
            i += 2;
            flag = -flag;
            p2 = p1;
            p1 = p1 + flag / i;
        }
        System.out.println(p1 * 4);
    }

    public static void gailv() {
        int N = (int) Math.pow(2, 25);
        double a[] = new double[N];
        double b[] = new double[N];
        for (int i = 0; i < N; i++) {
            a[i] = Math.random();
            b[i] = Math.random();
        }
        int cnt = 0;
        for (int i = 0; i < N; i++) {
            double c = a[i] * a[i] + b[i] * b[i];
            if (c <= 1) {
                cnt++;
            }
        }
        System.out.println(4.0 * cnt / N);
    }
}