How to format numbers on Android

Question

i am learning to program mobile aplications on Android. My first app is a unit converter. Everithing is working for now, but i have a question about formating numbers. I hava this code to get text from buttons and to convert the appropriet output:

if (bPrevodZ.getText() == "milimeter"){
    if (bPrevodDo.getText()=="kilometer"){
        String PomocnaPremenna = jednotkaZ.getText().toString();
        double cisloNaPrevod = Double.parseDouble(PomocnaPremenna);
        cisloNaPrevod = cisloNaPrevod*0.0000001;
        vysledok.setText(Double.toString(cisloNaPrevod));
    }

The final result is "cisloNaPrevod", but i have problems to show a good format of that number. For example: 12345 mm = 0,0012345 km this is good right ? :)

but if i convert: 563287 mm = 0.05632869999999995 this is bad :) i need it to show 0.0563287

Thx for any help

**Never** compare strings with `==`, use `.equals();`. Why? Read [this question](http://stackoverflow.com/questions/513832/how-do-i-compare-strings-in-java) — jlordo, Jan 06 '13 at 21:29

score 4 · Accepted Answer · answered Jan 06 '13 at 20:59

4

Use String.format:

String.format("%.6f", cisloNaPrevod);

answered Jan 06 '13 at 20:59

Chris

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I think it would be %.7f rather than %.6f, but correct nonetheless :) – Matt Le Fleur Jan 06 '13 at 21:02
Thx for the quick answer, but how can i use it in my code ? :) – MichalCh Jan 06 '13 at 21:13
Use it instead of your Double.toString() call – Chris Jan 06 '13 at 21:14
Now i have a new problem: if i convert 55 ly to meters it will show 5.203E17 but i need to show the whole number 520340175991944000 – MichalCh Jan 06 '13 at 21:34

badjr · Answer 2 · 2013-01-06T21:23:42.270

If you want your number to always have 6 significant figures, use

vysledok.setText(String.format("%.6g", cisloNaPrevod));

giving the result 0.0563287.

If you want to round to 6 numbers after the decimal place, use

vysledok.setText(String.format("%.6f", cisloNaPrevod));

giving the result 0.056329.

Here's some good resources that cover number formatting:

score 1 · Answer 3 · answered Jan 06 '13 at 21:47

1

If it's something you're going to do often, perhaps you should use DecimalFormat.

DecimalFormat df = new DecimalFormat("#.#######");

Then call:

df.format(someDoubleValue);

answered Jan 06 '13 at 21:47

snotyak

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How to format numbers on Android

3 Answers3