Rounding Currency to Nearest Dollar, how did you do it?

Question

The following piece of code works on all phones, in my production app, except for the Galaxy Nexus running 4.1.2. The Play store sent me the error, I will first post the code, and then the error:

    // Roughly formats the currency by loping off the decimal places (amount
// comes already rounded)
public static String formatCurrencyRound(double amount) {
    String currency = formatCurrency(amount); // Returns "$8.00"

    return currency.substring(0, currency.indexOf("."));
}

The Error:

java.lang.RuntimeException: Unable to resume activity {com.ootpapps.saving.made.simple/com.ootpapps.saving.made.simple.SavingsPlanOverview}: java.lang.StringIndexOutOfBoundsException: length=9; regionStart=0; regionLength=-1
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2575)
at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2603)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2089)
at android.app.ActivityThread.access$600(ActivityThread.java:130)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4745)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.StringIndexOutOfBoundsException: length=9; regionStart=0; regionLength=-1
at java.lang.String.startEndAndLength(String.java:593)
at java.lang.String.substring(String.java:1474)
at com.ootpapps.saving.made.simple.App.formatCurrencyRound(App.java:68)
at com.ootpapps.saving.made.simple.SavingsPlanOverview.updateSavingsPlanWidgets(SavingsPlanOverview.java:224)
at com.ootpapps.saving.made.simple.SavingsPlanOverview.onResume(SavingsPlanOverview.java:156)
at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1184)
at android.app.Activity.performResume(Activity.java:5082)
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2565)
... 12 more

If someone could propose a better way to round this currency string, or, a better way to round the raw number into a formatted string with no decimals, I'd hugely appreciate it. And again, this only fails on GNexus running 4.1.2 for some reason.

Thanks!

Edit Added formatCurrency code:

public static String formatCurrency(double amount) {
    NumberFormat currency = NumberFormat.getCurrencyInstance();

    return currency.format(amount);
}

Edit cont'd - Code I use which works to round currency to whole dollars:

public static String formatCurrencyWhole(double amount) {
    NumberFormat currency = NumberFormat.getCurrencyInstance();
    currency.setMaximumFractionDigits(0);
    currency.setMinimumFractionDigits(0);

    return currency.format(amount);
}

Answer 1

Firstly, currency should never, ever, ever be handled using doubles. You should use BigDecimal to keep precision. (See this question for more on that.)

That aside, you can use NumberFormat to get your String representation:

NumberFormat format = NumberFormat.getCurrencyInstance(Locale.US);
String result = format.format(amount);

.format() takes a double; if you end up using BigDecimal, use bigDecimal.doubleValue(). This answer provides some additional details in this area.

Answer 2

I think the format of the string was already $8

If the decimal doesn't exist:

currency.substring(0, currency.indexOf("."));

Will throw an IndexOutOfBoundsException.

The solution may be as simple as testing for the decimal before hand.

public static String formatCurrencyRound(double amount) { String currency = formatCurrency(amount); // Returns "$8.00"

if(currency.indexOf(".") != -1){
   return currency.substring(0, currency.indexOf("."));
}else{
   return currency;
}

}

------- EDIT ----------

As Ken (very smart guy) pointed out in the comments the key line in the stack trace is:

java.lang.StringIndexOutOfBoundsException: length=9; regionStart=0; regionLength=-1 at java.lang.String.startEndAndLength(String.java:593)

This error shows regionLength = -1 which means that the result of indexOf(".") was -1. ((".") didn't exist)

It also shows a string length of 9 which is what makes me think that the different seperator issue (that Ken also pointed out) might be the real problem. Unless the dollar amount was in the $10000000 range.

That's why I would like to see the code for formatCurrency(Double);

-----EDIT-----

As suspected you are using the default locale:

NumberFormat currency = NumberFormat.getCurrencyInstance();

The documentation has this to say about that:

http://developer.android.com/reference/java/util/Locale.html

"The default locale is not appropriate for machine-readable output. The best choice there is usually Locale.US – this locale is guaranteed to be available on all devices, and the fact that it has no surprising special cases and is frequently used (especially for computer-computer communication) means that it tends to be the most efficient choice too.

A common mistake is to implicitly use the default locale when producing output meant to be machine-readable. This tends to work on the developer's test devices (especially because so many developers use en_US), but fails when run on a device whose user is in a more complex locale."

Unless foreign currency is required by your app, use:

NumberFormat currency = NumberFormat.getCurrencyInstance(Locale.US);