Best way to print 2 doubles with same exponent

Question

How to best print 2 float numbers in scientific-notation but with same exponent? eg: I'd like to print numbers like this:

 1.234e-6 
11.234e-6

And I would like some function to detect automatically best exponent - that is smaller number always start at first decimal digit and bigger number prints how it must with same exponent. eg: 0.1 and 100 would print

   1.000e-1
1000.000e-1

But even when I ask explicitly for 2 decimal places String.format("%2.3e",11.234e-6) I got 1.123e-5

Addie

Answer 1

So far I come up with code bellow. It works as I want. But as you can see it is not exactly short or swift... It would be great if someone would point to some Java native functions which helps me to do it more elegant...

public static String repeat(int count, String with) {
    if(count<0){
        return "";
    }
    if(count>1e5){
        return "";
    }
    return new String(new char[count]).replace("\0", with);
}

public static String getFormattedDouble(double num,int posInt,int posFrac){
    if(num == 0) return "0"; // correct 0 value to be print only with one 0
    String sInt = repeat(posInt,"0");
    String sFrac = repeat(posFrac,"0");
    String sSing = num<0 ? "" : "+";
    DecimalFormat form = new DecimalFormat(sSing+sInt+"."+sFrac+"E0");
    String s = form.format(num);
    s = s.replace("E","e"); // I really thing capital E looks ugly
    return s;
}

public static String[] get2doublesSameExp(double a, double b){
    String[] s = new String[2];
    int expA;
    if(a == 0) expA = 0;
    else       expA = (int)Math.floor(Math.log10(Math.abs(a)));
    int expB;
    if(b == 0) expB = 0;
    else       expB = (int)Math.floor(Math.log10(Math.abs(b)));
    double expDif = Math.abs((double)expA-(double)expB);
    int fractPos = 3;
    if(expDif > 4) fractPos = 1; // too big exponent difference reduce fraction digits
    if(expDif > 6){
        // too big exponent difference print it normally it will be nicer
        s[0] = String.format("%1.3e",a);
        s[1] = String.format("%1.3e",b);
        return s;
    }
    int minExp = Math.min(expA,expB) - 1;
    s[0] = getFormattedDouble(a, expA - minExp, fractPos );
    s[1] = getFormattedDouble(b, expB - minExp, fractPos );
    // just text right justification
    String rightJust = repeat((int)expDif," ");
    int justIdx = expA < expB ? 0 : 1;
    s[justIdx] = rightJust + s[justIdx];
    return s;
}
String[] s = get2doublesSameExp(1.234e-6,11.234e-6);

Addie