Java DecimalFormat Scientific Notation Question

Question

I'm using Java's DecimalFormat class to print out numbers in Scientific Notation. However, there is one problem that I have. I need the strings to be of fixed length regardless of the value, and the sign on the power of ten is throwing it off. Currently, this is what my format looks like:

DecimalFormat format = new DecimalFormat("0.0E0");

This gives me the following combinations: 1.0E1, 1.0E-1, -1.0E1, and -1.0E-1.

I can use setPositivePrefix to get: +1.0E1, +1.0E-1, -1.0E1, and -1.0E-1, or whatever I like, but it doesn't affect the sign of the power!

Is there any way to do this so that I can have fixed length strings? Thanks!

Edit: Ah, so there's no way to do it using Java's existing DecimalFormat API? Thanks for the suggestions! I think I may have to subclass DecimalFormat because I am limited by the interface that is already in place.

Answer 1

This worked form me,

DecimalFormatSymbols SYMBOLS = DecimalFormatSymbols.getInstance(Locale.US);

    if (value > 1 || value < -1) {
        SYMBOLS.setExponentSeparator("e+");
    } else {
        SYMBOLS.setExponentSeparator("e");
    }

    DecimalFormat format = new DecimalFormat(sb.toString(), SYMBOLS);

Answer 2

Could you use printf() instead:

Format format = new DecimalFormat("0.0E0");
Double d = new Double(.01);
System.out.println(format.format(d));
System.out.printf("%1.1E\n", d);
d = new Double(100);
System.out.println(format.format(d));
System.out.printf("%1.1E\n", d);

Output:

1.0E-2
1.0E-02
1.0E2
1.0E+02

If you need to output to a String instead, you can use the information provided at Formatted Printing for Java (sprintf) to do that.

EDIT: Wow, that PrintfFormat() thing is huge and seems to be unnecessary:

OutputStream b = new ByteArrayOutputStream();
PrintStream p = new PrintStream(b);
p.printf("%1.1E", d);
System.out.println(b.toString());

I got the idea for the above code from Get an OutputStream into a String.