Built in methods for displaying Significant figures

Question

There\'s been a lot of questions on rounding by significant figures, and answers that that provides a new method to do the rounding, such as:

Rounding to an arbitrar

Answer 1

I found this nice way of doing it using String format. Apparently, users can specify maximum number of significant digits with a string format 'g' or 'G'. (http://developer.android.com/reference/java/util/Formatter.html)

This is if you just want to print it out.

public String toSignificantFiguresString(BigDecimal bd, int significantFigures){
    return String.format("%."+significantFigures+"G", bd);
}

This is if you want to convert it:

public BigDecimal toSignificantFigures(BigDecimal bd, int significantFigures){
    String s = String.format("%."+significantFigures+"G", bd);
    BigDecimal result = new BigDecimal(s);
    return result;
}

Here's an example of it in action:

    BigDecimal bd = toSignificantFigures(BigDecimal.valueOf(12345678.123456789), 10);
    System.out.println("bd: " + String.format("%f",bd));

NB: I'm using BigDecimal for calculation because double and float has a precision problems.)

Answer 2

Not quite right. To get it perfect:

public String toSignificantFiguresString(BigDecimal bd, int significantFigures ){
    String test = String.format("%."+significantFigures+"G", bd);
    if (test.contains("E+")){
        test = String.format(Locale.US, "%.0f", Double.valueOf(String.format("%."+significantFigures+"G", bd)));
    }
    return test;
}