How to display double without truncating to float in string formatting?

Question

I'm doing a Princeton's Algorithms course and first programming task requires to output the result in this way:

mean                    = 0.5929934999999997
stddev                  = 0.00876990421552567
95% confidence interval = [0.5912745987737567, 0.5947124012262428]

I thought about string formatting since no one in their right mind would count a number of spaces for indent:

    String confidence = "95% confidence interval";
    int width = confidence.length();
    String f = "%-".concat(String.valueOf(width)).concat("s = ");
    System.out.printf(f.concat("%f\n"), "mean", stats.mean());
    System.out.printf(f.concat("%f\n"), "stddev", stats.stddev());
    System.out.printf(f.concat("[%f, %f]"), confidence, stats.confidenceLo(), stats.confidenceHi());

But to my regret program truncates double to float:

mean                    = 0.591316
stddev                  = 0.009776
95% confidence interval = [0.589400, 0.593232]

So is there way to format double number in its entirety so to speak?

Answer 1

Use DecimalFormat for this occasion, something like:

    double mean = 0.592993499999999;
    NumberFormat formatter = new DecimalFormat("#0.000000000000000");
    System.out.println(formatter.format(mean));

Answer 2

Use 16 decimal place format "%.16f"

String confidence = "95% confidence interval";
int width = confidence.length();
String f = "%-".concat(String.valueOf(width)).concat("s = ");
System.out.printf(f.concat("%.16f\n"), "mean", stats.mean());
System.out.printf(f.concat("%.16f\n"), "stddev", stats.stddev());
System.out.printf(f.concat("[%.16f, %.16f]"), confidence, stats.confidenceLo(), stats.confidenceHi());

Answer 3

I used the String.valueOf(aDoubleNumber) method and changed the %f to %s in your printf statements. This worked for me.

public static void main(String[] args)
    {
        double mean = 0.5929934999999997;
        double stddev = 0.00876990421552567;
        double confidenceLo = 0.12345666612123;
        double confidenceHi = 0.123456784435369;

        String confidence = "95% confidence interval";
        int width = confidence.length();
        String f = "%-".concat(String.valueOf(width))
            .concat("s = ");

        // changed the %f to %s and used String.valueOf method to convert first
        System.out.printf(f.concat("%s\n"), "mean", String.valueOf(mean));
        System.out.printf(f.concat("%s\n"), "stddev", String.valueOf(stddev));
        System.out.printf(f.concat("[%s, %s]"), confidence,
                (String.valueOf(confidenceLo)), String.valueOf(confidenceHi));
    }

Output:

mean = 0.5929934999999997

stddev = 0.00876990421552567

95% confidence interval = [0.12345666612123, 0.123456784435369]