ADDITIONAL SYSTEM INFORMATION :
Any OS (tested on Ubuntu, and MacOS) and also tested on JDK8 and JDK17

A DESCRIPTION OF THE PROBLEM :
String.format takes tens of minutes to format a floating point if format specifies that it should be prepended with large number of 0. e.g. String.format("%09000000d", 2);

 

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
The code below took 1693 seconds (28 minutes) to return a string with 9 millions of chars. Same happens for 'f' format specifier. Time spent in format seems to increase quadric with the width of the generated string.

String s = String.format("%09000000d", 2);

However, the code below, that use 'x' as specifier returns way faster

String s = String.format("%09000000x", 2);


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
I expect the String.format to take similar amount of time regardless of formatter.


ACTUAL -
Returns correct result but very slow for 'd' and 'f' format specifier. Works as expected on for 'x' format specifier

---------- BEGIN SOURCE ----------
public class SystemFormat {
    public static void main(String[] args) {
        long t1 = System.currentTimeMillis();
        String sd = String.format("%0500000d", 2);
        long t2 = System.currentTimeMillis();
        String sx = String.format("%0500000x", 2);
        long t3 = System.currentTimeMillis();
        long diff1 = t2 - t1;
        long diff2 = t3 - t2;
        System.out.format("diff1 = %d%n", diff1);
        System.out.format("diff2 = %d%n", diff2);
    }
}

// outputs
// diff1 = 5927
// diff2 = 10
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
do not use String.format with larger specifier and prepend it with '0'.

FREQUENCY : always