Question

In Java, I am trying to get DecimalFormat to enforce the sign on an exponent sign. When it is positive I need a plus sign to appear. From what I have read this seems like a no brainer, but for myself it always throws up an error. I appreciate that there may be other methods to achieve my goal, but I would like to understand why in this specific method the error is occurring.

Double result = 123.456;
String sresult;

//This works
NumberFormat formatter = new DecimalFormat("0.00000E00");
        sresult = formatter.format(result); 
        System.out.println(sresult);        //1.23456E02

//This doesn't work
formatter = new DecimalFormat("0.00000E+00"); //Want to enforce the sign to appear
        sresult = formatter.format(result); 
        System.out.println(sresult);        //Expected 1.23456E+02 but error occurs

The error which is thrown up:

Exception in thread "main" java.lang.IllegalArgumentException:
Malformed exponential pattern "0.00000E+00"
    at java.text.DecimalFormat.applyPattern(Unknown Source)
    at java.text.DecimalFormat.(Unknown Source)
    at deccheck.main(deccheck.java:13)

I appreciate any insight.
Thanks,
Mark

Answer 1

Easy way:

formatter = new DecimalFormat("0.00000E00"); // Want to enforce the sign to appear
sresult = formatter.format(result);
if (!sresult.contains("E-")) { //don't blast a negative sign
    sresult = sresult.replace("E", "E+");
}
System.out.println(sresult);

Outputs 1.23456E+02 for your example.

But I don’t believe there’s a way to do it from inside the DecimalFormat pattern. Or at least the javadoc doesn’t indicate there is one.

Edit: trashgod brings up a good point. You’d probably want to get positive and negative signs from DecimalFormatSymbols if you plan on localizing this to different regions.

Edit 2: Andrei pointed out that E is also a localization variable. Shows what I know about localization.