Estimate PI with series expansion using loops

Question

I need to estimate PI by doing following series:

m(i) = 4( 1- 1/3 + 1/5 - 1/7 + 1/9 - 1/11 ...)

And this is what I've done so far:

 float mOfI = 1;
    System.out.println("i \t \t \t \t  m(i)" );
    for (int i = 1; i < n; i++) {
        float sum = i + 2;
        mOfI += 4 * (1 - (1 / sum));
        mOfI -= 4 * (1 - (1 / sum));
        System.out.println(i + "\t \t \t \t" +mOfI);
    }

I know I'm missing many rules here, but how can I make it to work correctly? I mean the math logic. How can I can solve it correctly?

Please Note the -+ in the series and all numbers are odd so i can't use i%2.

Estimated PI would be like 4.0000 , 3.1515, 3.1466 ..... and so on.

Also this question didn't received a well answer (there is no real PI value estimated)

Answer 1

Thanks all for your time, but i got the right solution:

  double start = 1;         // Start series
    double end   = 901;     // End series
    System.out.println("\ni           m(i)     ");
    System.out.println("---------------------");
    for (double i = start; i <= end; i += 100) {
        System.out.printf("%-12.0f", i);
        System.out.printf("%-6.4f\n", estimatePI(i));
    }
}

/** Method estimatePI */
public static double estimatePI(double n) {
    double pi = 0;      // Set pi to 0
    for (double i = 1; i <= n; i ++) {
        pi += Math.pow(-1, i +1) / (2 * i - 1);
    }
    pi *= 4;
    return pi;
}