There are behavioral differences between j.util.Formatter vs j.text.DecimalFormat for what one would expect the same answer,

For example,

var df = new DecimalFormat("0.00000");
df.setRoundingMode(RoundingMode.HALF_UP);
df.format(0.002485); // -> "0.00248"
String.format("%.5f", 0.002485); // -> "0.00249"

This is made further confusing since DecimalFormat has minimal specification regarding rounding, which is "DecimalFormat provides rounding modes defined in RoundingMode for formatting. By default, it uses RoundingMode.HALF_EVEN."

At a minimum, DecimalFormat needs to have a overhaul of the current rounding section to address the 3 main issues
- No spec regarding what type of format, the rounding is performed under, causing confusion in the past (JDK-7131459, etc.).
- No spec regarding the precision of the DecimalFormat beyond the pattern. If I format a fractional value with 50 fractional digits, even if my pattern supports that many digits, I lose most of the precision
- No spec when formatting to less digits than the input value with certain rounding modes

These should all be added to a new rounding mode section.

As to the discrepancy in behavior between Formatter and DecimalFormat, DecimalFormat has had this discrepancy for 10+ years, which raises concerns for compatibility issues if the classes are aligned. It is safest to not align the classes, however, standardizing the behavior for a future LTS release is a possibility.